How to Read a Cannabis COA
October 14, 2026
A certificate of analysis, or COA, is the lab report behind a jar of cannabis. An independent, licensed lab takes a sample from a batch, measures what is in it, checks it for things that should not be, and signs the result. Most shops will show you one if you ask, and more and more packages carry a QR code that opens it on your phone. Very few people read past the first number.
We think that is a shame.
The guides that rank for this question, from testing labs and clinics, agree on the outline: check the header, read the potency table, glance at the terpenes, confirm the safety tests passed, watch for signs of a fake. New Jersey’s cannabis regulator even prints a pocket card that walks through those steps. We will follow the same route. Then we want to read the report the way a buyer of good flower should, as a record of how old the cannabis is and how it was treated after harvest, because the clues are already printed there and nobody points at them.
The header and the batch number
The top of the page names the lab, the producer, the product and a batch or lot number, along with the dates the sample was collected and the report was issued. Match the batch number to the one on your package. If they differ, the report describes some other flower, and everything below it is beside the point.
Check that the lab and the producer are different companies with different addresses. A report should also be signed or approved by someone at the lab, usually at the bottom, and carry the lab’s license or accreditation number.
The potency table
Here you will find THCA, THC, and usually CBDA, CBD and a handful of minor cannabinoids, often in two columns, one in percent and one in milligrams per gram. The conversion is simple: 10 mg/g is 1%. The line most labels repeat is Total THC, which is the THC already present plus the THCA multiplied by 0.877, a correction for the small piece of the molecule that leaves as carbon dioxide when heated. Our guide to THC percentage explains that arithmetic and why the number deserves less faith than it gets. Anything above roughly thirty percent on whole flower is worth a second look at who did the testing.
The minor lines are where the curious reader lingers. A measurable figure for CBG says something about harvest timing and breeding, as our page on CBG describes, and a real THCV figure is close to a fingerprint of African ancestry, which we cover in What Is THCV?
ND, LOQ, and the meaning of nothing
Every lab instrument has a floor. The limit of detection (LOD) is the smallest amount it can tell apart from zero, and the limit of quantitation (LOQ) is the smallest amount it can measure with confidence. A result of ND means not detected, below the floor. <LOQ means something is there but too little to put a number on. Neither one means zero, and two labs with different equipment can report the same flower differently.
Terpenes, when they appear
Many states do not require a terpene panel, so its presence alone tells you the producer paid for something optional. Read the total first. Around 2% by weight or more points to real aromatic density. Then look at the spread: four or five terpenes in meaningful proportion usually smell more layered than one compound towering over the rest. Our guide to terpene profiles translates the names into what you will actually smell.
The safety panel
This is the part of the report that protects you, and on a legal-market COA it is usually long. Microbial tests look for organisms such as E. coli and Salmonella, and for mould and yeast counts. Mycotoxin tests look for the poisons certain moulds leave behind, aflatoxins and ochratoxin among them. There are heavy metals (lead, arsenic, cadmium, mercury), which a cannabis plant pulls readily from soil, and a pesticide screen that can run to dozens of compounds. Extracts add residual solvents. Each line should read Pass or ND against an action limit that the state sets.
A report that shows potency and nothing else is a sales document.
Reading it as a clock
The usual guides stop at pass or fail. A COA is a snapshot of one day, though, and it carries enough small details to tell you a good deal about time.
Start with the dates. The sample date is when the flower was pulled for testing, which is close to when it finished curing. Compare it with the packaging date on your jar and with today. Flower loses aroma every week after the cure, as we explain in How to Store Cannabis Flower, so a report from eight months ago describes a flower that no longer exists in quite that form. The terpene total in particular was true on the sample date and has only fallen since.
Next, compare THC with THCA. In freshly cured flower that has been kept cool and dark, nearly all of it is still THCA, and the neutral THC line is small by comparison. Heat and age convert one into the other slowly. A THC figure that is unusually large next to its THCA suggests flower that spent time somewhere warm before it was tested, whether a hot drying room or a long wait in a warehouse.
Then find CBN. THC turns into CBN when oxygen works on it over months, which our page on CBN describes in detail, and recently harvested, properly stored flower carries very little. A noticeable CBN figure on a report for flower sold as fresh is a contradiction worth asking about.
Last, the moisture line, if the lab ran one. Some reports give moisture content as a percent; some give water activity, a figure between 0 and 1. Craft growers cure toward a water activity of roughly 0.55 to 0.62. Well below that, the flower was dried hard, which damages flavor and, as the THC percentage guide points out, nudges potency upward on paper by removing weight. Well above it, and the batch was packed wet.
None of these numbers proves anything alone. Read together, with the dates beside them, they tell you whether the report and the flower in your hand are describing the same thing, and they say more about the care a grower took than the potency figure ever will.
Signs a report deserves doubt
A missing batch number. A lab whose name you cannot find with a license attached. A potency figure printed to two decimal places with no safety panel beneath it, or a PDF whose fonts change halfway down the page. Totals that do not add up when you run the 0.877 sum yourself. The same report attached to three different cultivars on a brand’s website. Any one of these is reason to ask the shop for the original, straight from the lab. A good producer will send it gladly, because the paperwork is part of what they are proud of.
Our position
We would like to see every craft producer print the sample date as prominently as the THC figure, and we suspect the good ones would welcome it.
Until then, use the COA to rule out what is unsafe, to check that the batch is the batch, and to learn from its dates and small lines how the flower has lived since harvest. Then open the jar, because the press test and the first breath of aroma described in What Makes Cannabis Craft will confirm or contradict the paper within seconds, and when they disagree, believe the flower.