How to Read a Marijuana Lab Report: THC, THCA, Terpenes, Contaminants and COAs Explained

A marijuana lab report can tell you far more than the THC and CBD percentages printed on the front of a package.

A full certificate of analysis, commonly called a COA, can show how much THC, THCA, CBD, CBG, CBN and other cannabinoids were measured in a batch; which terpenes were detected; whether pesticides, solvents, heavy metals or microorganisms were found; how much moisture is present; and whether the sample passed the safety standards required in that jurisdiction.

But reading one is not always straightforward.

A flower sample might contain 25% THCA but only 1% delta-9 THC while listing “Total THC” at approximately 23%. A contaminant might appear as “ND,” “<LOD” or “<LOQ.” Terpenes may be expressed as percentages on one report and milligrams per gram on another. A product may receive a passing result even though a detectable amount of a contaminant is present.

None of those results are necessarily contradictory.

This guide explains how marijuana laboratory testing works, what the major numbers on a COA mean and what a lab report can — and cannot — tell you about a product.

Marijuana Lab Reports at a Glance

Section of the COAWhat to Look ForWhat It Tells You
Batch information	Batch or lot number, product name, sample ID	Whether the COA actually belongs to your product
Cannabinoids	THC, THCA, CBD, CBDA, CBG, CBN and others	The measured cannabinoid composition
Total THC	THC + converted THCA	Estimated potential THC after decarboxylation
Terpenes	Myrcene, limonene, pinene, caryophyllene and others	The measured aromatic profile
Pesticides	Result and regulatory action level	Whether tested pesticide residues exceeded applicable limits
Residual solvents	Butane, propane and other tested solvents	Whether solvent residues exceeded applicable limits
Heavy metals	Lead, cadmium, arsenic, mercury and others	Whether tested metals exceeded applicable limits
Microbial testing	Mold, bacteria and other microorganisms	Whether the sample met microbial standards
Mycotoxins	Toxins produced by certain fungi	Whether tested mycotoxins exceeded limits
Water activity	Usually reported as Aw	How much water is available to support processes including microbial growth
Moisture	Usually a percentage	The overall amount of water in the sample
LOD/LOQ	Detection and quantitation limits	How sensitive the laboratory’s method is
Pass/Fail	Individual tests and/or overall result	Whether the sample met that jurisdiction’s regulatory requirements

What Is a Certificate of Analysis?

A certificate of analysis is the laboratory report produced after a sample of marijuana or a marijuana product is analyzed.

In regulated markets, laboratories generally test a representative sample taken from a larger production batch. That distinction is important: the laboratory typically does not test the exact flower in every jar, every gummy in every package or every cartridge sold at a dispensary.

The COA instead reports the results obtained from the sample selected to represent that batch.

California’s Department of Cannabis Control, for example, requires regulated marijuana batches to undergo laboratory testing before retail sale and says laboratories test for cannabinoids, residual solvents and processing chemicals, pesticides, heavy metals, microbial impurities, mycotoxins, moisture, water activity and foreign material. Results are reported on a COA.

Testing requirements differ by state, so not every COA will contain exactly the same analytes or use the same limits.

First: Make Sure the COA Actually Matches the Product

Before looking at THC or terpenes, check the identifying information.

The most important number is usually the batch or lot number. The number on the package should match the batch listed on the COA. Also look for the product name or matrix, producer or manufacturer, laboratory name, sample identification number and testing dates.

A QR code on a package can make finding the COA easier, but the presence of a QR code alone does not prove that the report corresponds to the product in your hand. The identifying information should match.

When possible, consumers can also verify that the laboratory is currently licensed or certified by the applicable state regulator. Some jurisdictions also require laboratories to maintain ISO/IEC 17025 accreditation.

California illustrates how detailed a regulatory COA can be. Its 2026 rules require information including the laboratory and license number, producer or manufacturer information, batch number, matrix and unique sample identifiers, collection and testing dates, analytical methods, instrumentation and the corresponding limits of detection and quantitation.

That makes the batch number one of the most useful pieces of information on the entire document.

THC vs. THCA: Why Marijuana Lab Reports Show Both

This is probably the most misunderstood part of a marijuana COA.

Fresh marijuana flower generally contains much more tetrahydrocannabinolic acid (THCA) than delta-9 tetrahydrocannabinol (THC).

THCA is the acidic precursor to THC. It does not produce the familiar THC intoxication in its original form.

Heat changes that.

When marijuana is smoked, vaporized or heated during cooking, THCA undergoes decarboxylation, losing part of its molecular structure and converting into THC.

That is why a flower COA can show something like:

CannabinoidResult
THCA	25.0%
Delta-9 THC	1.0%
Total THC	22.9%

The 25% THCA number is not simply added to the 1% THC number.

How Total THC Is Calculated

A widely used calculation is:

Total THC = Delta-9 THC + (THCA × 0.877)

Washington’s marijuana testing regulations use this formula, as do federal hemp rules when calculating potential total delta-9 THC.

For flower containing:

25% THCA

and

1% delta-9 THC

the calculation is:

25 × 0.877 = 21.925

Then:

21.925 + 1 = 22.925% Total THC

The resulting total THC is therefore approximately 22.9%.

Why Is THCA Multiplied by 0.877?

THCA and THC do not have identical molecular weights.

During decarboxylation, THCA loses carbon dioxide. The resulting THC molecule weighs less than the original THCA molecule.

The 0.877 conversion factor accounts for that difference.

Federal regulators describe this calculation as the maximum, potential or theoretical total THC assuming complete conversion of THCA. Actual conversion is not necessarily 100% in real-world use.

That distinction matters.

A COA showing 25% total THC does not mean that a person smoking one gram of that flower will absorb exactly 250 milligrams of THC. Decarboxylation may be incomplete, material can be lost during heating or combustion, and only part of the THC delivered by a product ultimately reaches systemic circulation.

Total THC is primarily a chemical potency measurement, not a prediction of the exact dose a consumer will absorb.

Percentage vs. Milligrams per Gram

Marijuana flower and concentrates are commonly reported as percentages, while laboratories may also express concentrations in milligrams per gram (mg/g).

The conversion is simple:

1% by weight = 10 mg/g

That means:

PercentageApproximate concentration
0.5%	5 mg/g
1%	10 mg/g
10%	100 mg/g
20%	200 mg/g
25%	250 mg/g
30%	300 mg/g
80%	800 mg/g

A flower containing 24% total THC therefore contains approximately 240 mg of potential total THC per gram of material.

Again, that does not mean smoking the entire gram delivers 240 mg into the bloodstream.

What Does mg/mL Mean?

Liquid products such as tinctures, oils and beverages may report cannabinoids or terpenes in milligrams per milliliter (mg/mL) rather than milligrams per gram. This expresses how much of the compound is present in a given volume of liquid.

Do not automatically convert mg/mL to mg/g unless the product’s density or the reporting basis is known. Weight and volume are different measurements.

Why Edible COAs Use Milligrams Instead

For marijuana edibles, beverages, capsules and similar products, percentage is usually much less useful.

What matters is the amount contained in a serving and package.

A COA might report:

THC per serving: 5 mg

THC per package: 50 mg

If the package contains 10 gummies and the THC is distributed evenly, that corresponds to an average of 5 mg per gummy.

This is why consumers should not compare a “20% THC” flower directly with a “10 mg THC” gummy as though the two numbers represent the same measurement.

One describes concentration by weight. The other describes an amount of THC expressed by mass.

For more on why swallowed THC behaves differently, see our guide to How Marijuana Edibles Work: Dosage, Onset, Duration and Why They Feel Different.

What About CBD and CBDA?

The same basic principle applies to cannabidiol (CBD).

Marijuana and hemp plants can contain cannabidiolic acid (CBDA), which converts into CBD through decarboxylation.

Total CBD is commonly calculated as:

Total CBD = CBD + (CBDA × 0.877)

Washington regulations explicitly use that calculation.

So a COA may separately display:

CBD

CBDA

Total CBD

Those are related measurements, not three entirely separate quantities that should be added together.

What Do CBG, CBGA, CBC, CBN and THCV Mean on a COA?

Many modern laboratory panels measure considerably more than THC and CBD.

Depending on the laboratory and jurisdiction, a report may include cannabinoids such as:

CBG and CBGA, CBN, CBC, THCV, CBDV, delta-8 THC or other minor cannabinoids.

The presence of these compounds can provide a more complete chemical profile of a product.

They should not, however, be interpreted as though every detected cannabinoid has a well-established effect at the measured concentration.

Human evidence differs enormously from cannabinoid to cannabinoid.

Our Cannabinoids Explained guide examines THC, CBD, CBG, CBN, CBC, THCV, acidic cannabinoids and several lesser-known compounds in greater detail.

What Does “ND” Mean on a Marijuana Lab Report?

ND generally means Not Detected.

That does not necessarily mean that the substance is proven to be completely absent.

It means the laboratory did not detect it above the sensitivity threshold of the analytical method.

ND: The analyte was not detected under the laboratory’s reporting criteria.

<LOD: The concentration is below the method’s limit of detection.

<LOQ: The analyte is below the concentration the laboratory can reliably quantify.

Exact reporting conventions can differ by laboratory, so check the COA’s definitions or notes when available.

Understanding that distinction requires knowing two additional terms: LOD and LOQ.

LOD vs. LOQ: One of the Most Important Parts of a COA

The limit of detection (LOD) is approximately the lowest amount of a substance that the analytical method can distinguish from its absence.

The limit of quantitation (LOQ) is the lowest concentration that can be measured reliably enough to report as a quantitative result.

California’s regulatory definitions describe LOD as the lowest quantity distinguishable from absence within a stated confidence limit, while LOQ is the minimum concentration that can be reliably quantified while meeting defined requirements for bias and imprecision.

Suppose a laboratory has:

LOD: 0.02 µg/g

LOQ: 0.05 µg/g

A substance below 0.02 µg/g may appear as ND.

A signal between the detection and quantitation limits could potentially be detectable but too low to measure reliably. Depending on the reporting system, it might be shown as <LOQ, meaning less than the limit of quantitation.

So:

ND does not necessarily mean absolute zero.

And:

<LOQ does not necessarily mean the substance is absent.

It means the concentration is below the level the laboratory can reliably quantify under that method.

What Is an Action Level?

An action level is different from the LOD and LOQ.

It is a regulatory threshold used to determine whether a sample passes or fails a particular test.

Imagine a hypothetical contaminant with an action level of 0.50 µg/g.

A laboratory might measure:

0.08 µg/g — PASS

The contaminant was detected, but its concentration remained below the regulatory threshold.

That is why “detected” and “failed” do not mean the same thing.

Conversely, a contaminant measured above the applicable action level can trigger a failed result.

The specific action levels differ according to the compound, product type and jurisdiction.

How to Read the Terpene Section

A terpene panel may include compounds such as:

myrcene, limonene, beta-caryophyllene, alpha-pinene, beta-pinene, linalool, terpinolene, humulene and ocimene.

Results are commonly reported as either percentages or milligrams per gram.

The same conversion applies:

1% = 10 mg/g

So:

0.50% limonene = approximately 5 mg/g

A COA may also provide a total terpene percentage, calculated from the terpenes included in that laboratory’s analytical panel.

This number requires some caution.

Two laboratories do not necessarily measure the exact same terpene panel. A laboratory analyzing 20 terpenes could therefore produce a different “total terpene” result than a laboratory measuring a broader collection of compounds.

A higher terpene percentage also does not automatically mean stronger marijuana.

THC remains the primary intoxicating cannabinoid in conventional marijuana, while aroma, flavor and effects can depend on numerous compounds and individual factors.

Our complete Cannabis Terpenes Explained guide examines the major terpenes and what human and preclinical research actually says about their effects.

How to Read Contaminant Testing

Potency is only one part of marijuana laboratory testing.

Depending on state requirements and product type, a COA may contain several major safety panels.

TestWhat It Looks ForWhat to Check
Pesticides	Residues of specified agricultural chemicals	Result compared with the action level
Residual solvents	Solvents remaining after manufacturing or extraction	Pass/fail and measured concentration
Heavy metals	Metals such as lead, cadmium, arsenic and mercury	Result compared with the applicable limit
Microbial impurities	Specified fungi and bacteria	Pass/fail or quantitative result
Mycotoxins	Toxic compounds produced by certain fungi	Result compared with action level
Foreign material	Unwanted physical or biological material	Pass/fail

The exact compounds tested can vary substantially by state.

California, for example, regulates pesticides, residual solvents, heavy metals, microbial impurities, mycotoxins and other categories. Its heavy-metal rules establish separate action levels for certain inhalable and non-inhalable products.

That is an important reason not to compare a “PASS” from two jurisdictions without considering what each jurisdiction actually requires laboratories to test.

What Does a Pesticide “Pass” Mean?

A pesticide pass means the sample satisfied the regulatory criteria for the pesticides included in the applicable testing panel.

It does not necessarily mean a laboratory proved that no molecule of any pesticide exists anywhere in the product.

Depending on the rule, some compounds may be required to remain below an action level, while others may need to remain below detection or quantitation thresholds.

The details matter.

California’s pesticide regulations, for example, establish compound-specific action levels and laboratory quantitation requirements.

What Are Residual Solvents?

Residual solvent testing is particularly relevant to marijuana extracts and manufactured products.

Solvents may be used during extraction or processing, and laboratory testing can determine whether specified solvent residues remain above regulatory thresholds.

A COA may list multiple solvents individually and provide a concentration, action limit and pass/fail result.

A detected solvent is not automatically a failed product. The result must be compared with the applicable regulatory limit.

What Does Heavy-Metal Testing Look For?

Marijuana testing programs commonly include metals such as:

lead, cadmium, arsenic and mercury.

Plants can take up metals from soil, water, fertilizers and other environmental sources, while processing and manufacturing can introduce additional opportunities for contamination.

The allowable levels are not necessarily identical across product types or states.

California, for example, applies different limits for certain metals depending on whether a marijuana product is inhalable or non-inhalable.

The important number on the COA is therefore not merely whether a metal was detected, but how the measured concentration compares with the applicable action level.

Microbial Testing and Mycotoxins

Marijuana products may also be tested for microbial contamination.

The organisms included in a required panel differ by jurisdiction, but testing can include specified pathogenic bacteria or fungi.

Mycotoxins are slightly different.

They are toxic substances produced by certain fungi. A laboratory can therefore test for particular mycotoxins even when the report has a separate microbial-testing section.

Consumers reading a COA should treat microbial impurities and mycotoxins as related but distinct categories.

Moisture Content vs. Water Activity

These two measurements sound similar but answer different questions.

Moisture content describes how much water is present in the material overall.

Water activity, expressed as Aw or aW, measures the availability of water in a material. Water that is chemically or physically bound does not behave the same way as freely available water.

The U.S. Food and Drug Administration explains that microorganisms generally grow more readily as water activity increases because more water is available to them.

This distinction is especially useful for marijuana flower.

Two samples could have similar moisture percentages but somewhat different water activity depending on how water is associated with the plant material.

California and Washington both use 0.65 Aw as a maximum water-activity threshold for regulated dried marijuana flower under their respective rules, while both use 0.85 Aw for certain solid edible products.

Those numbers are regulatory examples, not universal limits for every state.

Also remember that 0.65 Aw does not mean 65% moisture. They are different measurements.

Dry Weight vs. “As Received” Results

Another detail that can complicate comparisons is whether cannabinoid concentration is calculated on a dry-weight basis or from the material as received.

Removing moisture mathematically increases the percentage of everything else in the remaining dry material.

California’s regulations, for example, specify a calculation for converting cannabinoid measurements to dry-weight percentages in certain harvest-batch testing.

Other regulatory systems can require samples to be analyzed on an as-is or as-received basis.

That means two potency numbers should not automatically be compared without checking how each result was calculated.

This issue is particularly important when evaluating hemp because federal THC limits are based on dry weight.

Does a COA Tell You Exactly How Potent Your Marijuana Is?

It gives you useful laboratory evidence about the batch, but it should not be treated as a perfect measurement of every individual piece of marijuana in that batch.

Flower is a biological material.

Cannabinoid and terpene concentrations can vary within a plant, between flowers and across a production batch. Sampling therefore matters considerably.

Concentrates and manufactured liquids may be easier to homogenize than flower.

A 2025 study examining 277 retail marijuana flower and concentrate products purchased from 52 Colorado dispensaries illustrates the issue. Researchers independently retested the products and found that 96% of concentrates were within ±15% of their labeled THC value, compared with 56.7% of flower products.

Earlier research has also identified substantial differences between labeled and independently measured flower potency.

The National Institute of Standards and Technology has established a Cannabis Laboratory Quality Assurance Program specifically to improve measurement comparability and laboratory competence. Its research has examined cannabinoid testing, moisture and toxic-element measurements, among other areas.

This does not make COAs useless.

It means that a number such as 24.83% THC should not be interpreted as though every portion of the entire batch contains precisely 24.83%.

What Is Measurement Uncertainty?

Laboratory measurements are not infinitely precise. Some reports include a measurement uncertainty, often expressed as a plus-or-minus value.

For example, a result might be reported as:

Total THC: 0.28% ± 0.04%

The uncertainty value represents the estimated range associated with the measurement rather than a second measurement of THC.

Measurement uncertainty is especially important in regulatory testing when a result is close to a legal or regulatory threshold. The U.S. Department of Agriculture, for example, requires measurement uncertainty to be calculated and reported for hemp THC compliance testing.

Not every consumer marijuana COA displays uncertainty in the same way, and state requirements differ.

Can Marijuana Labs Produce Different Results?

Yes.

Differences can result from sampling, sample preparation, moisture, calibration, analytical methods, instrumentation and normal measurement uncertainty.

There have also been regulatory concerns about commercial incentives surrounding potency results.

California’s Department of Cannabis Control said in 2026 that weaknesses in the state’s existing track-and-trace and testing system can enable “lab shopping.” The agency has proposed regulatory changes intended to prevent multiple laboratories from being used to obtain and select favorable results from the same batch.

Consumers therefore should view laboratory testing as an important quality-control tool while recognizing that no analytical system is perfectly immune to sampling or measurement problems.

What Does “Pass” Actually Guarantee?

A passing COA means the tested sample met the applicable standards for the analyses required under that testing program.

It does not mean that scientists have proven the product contains absolutely no contaminants.

It also does not mean that every possible chemical substance was tested.

A laboratory can only report results for the analytes included in its testing method.

For example, a product could truthfully pass a required pesticide panel without having been analyzed for every pesticide or environmental contaminant that exists.

The strongest interpretation of “PASS” is therefore:

The tested sample satisfied the applicable requirements for the substances and limits included in that testing program.

A Hypothetical Marijuana COA, Explained

Consider a flower COA showing:

ResultMeasurement
THCA	24.8%
Delta-9 THC	1.2%
Total THC	22.95%
CBD	<LOQ
CBG	0.6%
Total terpenes	2.1%
Water activity	0.58 Aw
Pesticides	Pass
Heavy metals	Pass
Microbial testing	Pass
Mycotoxins	Pass

Here’s what that means.

The flower contains mostly THCA rather than already-active THC.

Using the standard calculation:

24.8 × 0.877 = 21.75

Adding the existing 1.2% THC produces approximately:

22.95% Total THC

The CBD result of <LOQ means the concentration was below the laboratory’s reliable quantitative reporting threshold. It does not necessarily prove there is literally zero CBD.

A total terpene result of 2.1% means the terpenes included in that laboratory’s panel totaled approximately 21 mg/g.

The water activity of 0.58 Aw falls below the 0.65 threshold used for dried flower in states such as California and Washington.

Finally, the contaminant panels passed the applicable regulatory criteria.

That is a much more complete picture of the product than simply saying it is “23% THC marijuana.”

What a Marijuana COA Cannot Tell You

A lab report is useful, but several important questions fall outside its capabilities.

QuestionCan a COA Answer It?
How much THC and THCA were measured?	Yes
Which tested terpenes were present?	Yes
Did the sample pass required contaminant tests?	Yes
Will this product feel strong to you personally?	No
Will it make you relaxed, energetic or sleepy?	Not reliably
Will every flower in the batch have identical potency?	No
Is the product completely free of every possible contaminant?	No
How much THC will your body actually absorb?	No
Does a high THC percentage mean higher overall quality?	No
Will two products with the same THC percentage feel identical?	No

This is an important distinction.

A COA describes measured chemistry.

It does not reliably predict an individual’s subjective experience.

Tolerance, dose, consumption method, other cannabinoids, terpenes, individual biology and numerous other variables can influence how marijuana feels.

Is Higher THC Always Better?

No.

THC percentage is one useful measurement, but it is not a comprehensive quality score.

A higher-THC flower is not automatically fresher, better grown, more aromatic, better cured or more enjoyable.

It also does not necessarily have a richer terpene profile.

Two products can both contain 25% total THC while possessing very different concentrations of minor cannabinoids and aromatic compounds.

For consumers interested in understanding marijuana chemistry rather than simply chasing the largest number on the label, the entire COA is considerably more informative than the THC percentage alone.

What Should You Look at First on a COA?

For most consumers, a useful order is:

1. Confirm that the batch number matches the product.
2. Check whether the sample passed required testing.
3. Look at Total THC rather than THCA or delta-9 THC alone when evaluating flower’s potential THC content.
4. Review CBD and other cannabinoids.
5. Examine the terpene profile if one was tested.
6. Review pesticides, solvents, heavy metals, microbial impurities and mycotoxins.
7. Check water activity and moisture when relevant.
8. Look at the testing date, laboratory and LOD/LOQ if you want to understand the results in greater detail.

Once you understand those sections, even a complicated multi-page marijuana COA becomes relatively easy to interpret.

Scientific and Government Sources

This guide was prepared using current marijuana testing regulations, federal guidance and peer-reviewed laboratory research, including:

California Department of Cannabis Control — Testing Laboratories

California Department of Cannabis Control — Medicinal and Adult Use Cannabis Regulations

Washington State — WAC 314-55-102, Marijuana Laboratory Testing Requirements

U.S. Department of Agriculture — Hemp Testing and Total THC Guidance

National Institute of Standards and Technology — Cannabis Laboratory Quality Assurance Program Cannabinoid Report

U.S. Food and Drug Administration — Water Activity in Foods

Peer-Reviewed Study — Accuracy of Labeled THC Potency Across Flower and Concentrate Cannabis Products