How to read a lab sheet (COA)

By StashLog · 2026-09-28

What each section of a cannabis Certificate of Analysis is, which numbers matter when you are choosing a jar, what total terpenes does and does not tell you, and how to spot an old batch.

Every legal jar was tested before it reached the shelf, and the lab's report is called a Certificate of Analysis, or COA. It is usually a few pages of tables, most of it there for the state rather than for you. This guide walks through a typical sheet, says which numbers deserve your attention, and is honest about what the sheet cannot tell you. Labs and states differ, so take the order below as typical rather than fixed.

The header: whose sample, and when

The top of the sheet identifies what was tested. Look for:

• The testing lab, with its state licence number and usually an accreditation mark. The lab is independent of the grower.
• The client, which is the grower or processor that sent the sample, and the product name as the client registered it.
• The batch or lot number. This is the line that connects the sheet to the package in your hand. If the lot number on your label does not match the lot on the sheet, the sheet is about a different batch.
• The matrix, meaning the kind of sample: flower, concentrate, vape oil, edible.
• Dates: when the sample was collected, when the lab received it, and when the results were reported. Some sheets also carry the harvest date.

The dates matter more than they look: a sheet describes the sample on the day it was tested, and nothing that happens after.

Potency: the cannabinoid table

The potency section lists each cannabinoid the lab measured, usually as both a percent and in milligrams per gram. The two are the same ratio written two ways: 10 mg/g is 1%, so 245 mg/g of THCa is 24.5%.

On flower you will nearly always see a large THCa number and a small THC number. THCa is THC before heat; most of it converts when it is heated. That is why the sheet also prints Total THC, which is worked out with a standard formula:

Total THC = THC + (THCa × 0.877)

The 0.877 is not a fudge factor. THCa is a heavier molecule than THC because it carries an extra carboxyl group, and 0.877 is the ratio of their molecular weights. The same arithmetic gives Total CBD from CBD and CBDa.

Two details worth knowing:

• ND means not detected, and <LOQ means below the limit of quantitation: something may be there, but not enough for the method to put a number on it.
• Some labs report flower on a dry-weight basis, correcting for the water in the sample, and some report it as received. Dry-weight numbers come out a little higher. The sheet says which one it used, usually in small print near the table.

The minor cannabinoids (CBG, CBN, CBC, THCV) often sit at a percent or less. CBN is worth a glance, for a reason covered below.

Terpenes: the aroma panel

If the lab ran a terpene panel, you get a second table: each terpene the lab looked for, its amount, and a total terpenes line at the bottom.

What the total tells you is simple and useful: how much of the sample's weight is made of the terpenes on that lab's panel. Around 1–2% is common for flower; concentrates can run much higher.

What the total does not tell you is just as important:

• It only counts what the lab looked for. A panel of ten terpenes and a panel of forty will total differently on the same jar. Compare totals between sheets from the same lab, not across labs.
• It is not the whole smell. Terpenes are the biggest group of aroma compounds a lab measures, but not the only ones behind what a jar smells like. Oswald and colleagues (ACS Omega, 2023) found that some of the most distinctive cannabis aromas came from minor compounds, including sulphur-containing ones, that a standard terpene panel does not measure.
• It is not a verdict on the experience. A higher number is more of those compounds by weight. It is not a score, and nobody has shown that it predicts how a jar will go for you.

The shape of the panel, which terpenes lead and in what proportion, is what StashLog draws as each jar's ring: one arc per terpene, each as long as its share. Similar rings mean similar measured profiles. That is all the ring claims.

Safety: the pass/fail pages

The rest of the sheet is safety testing, and it is usually a list of pass or fail results against the state's limits. Depending on the state and the product, expect some of these:

• Microbial: mould, yeast and bacteria such as E. coli and salmonella.
• Mycotoxins: toxins some moulds produce, such as aflatoxins and ochratoxin.
• Heavy metals: lead, arsenic, cadmium and mercury.
• Pesticides: a state-set list of residues, often dozens of lines long.
• Residual solvents: for concentrates made with butane, propane, ethanol and similar, what is left afterwards.
• Moisture or water activity: for flower, because too much water invites mould.
• Foreign matter: hair, insects, stems and similar.

For a buyer the rule is short: every required test should say pass, and a batch that fails one cannot be sold as it is. A line marked "not tested" may simply not be required for that product in your state.

Which numbers matter when you are choosing

If you only have a minute at the counter, look at four things:

1. The lot number matches your package. Otherwise you are reading about somebody else's jar.
2. The dates. How long ago was it harvested, and how long ago was it tested?
3. The terpene panel's shape and total, compared with sheets from the same lab for jars you already know you liked.
4. Every safety line passes.

Total THC is printed biggest, and it is the number this app cares about least: it tells you content, not whether you will rate the jar well. StashLog scores jars on your own ratings of taste, smell and how they hit.

How to spot an old batch

A sheet is a snapshot, and flower keeps changing after it. Terpenes are volatile and evaporate over time, faster when warm or open to air. THC slowly breaks down into CBN with time, heat and light. Neither of those changes shows up on a sheet written before they happened.

Signs a batch has been around a while:

• A long gap between harvest and package date, or between the test date and the day you are buying.
• A CBN number that stands out against other sheets from the same lab. It is a hint about age and storage, not proof on its own.
• A low terpene total compared with earlier lots of the same product from the same lab. This is where writing things down pays off.

That last comparison is what the StashLog lot ledger is for: every lot of the same product you have logged, lined up with its sheet, so you can see whether this one looks like the lot you loved or the one you did not.