How to Read a Cannabis COA (or Scan It in 2 Seconds)

Every legal cannabis product comes with a Certificate of Analysis — a COA. It’s the lab document that says what’s actually in the jar: cannabinoids, terpenes, and the contaminants that are supposed to be absent. Most of the time it’s a QR code on the label or a PDF you never open. And most of the time, the single number people read off it — the big bold THC percentage — is the one number that doesn’t mean what they think it means.

This is a field guide to reading the document. What each section is, what counts as a high or low number, the THCA-to-THC math the label makes you do in your head, and why an old COA is quietly lying to you about terpenes. At the end, the two-second version.

What a COA actually contains

A complete COA has four parts. Read them in this order and you’ll never be fooled by packaging again.

• Sample identity — the product name, batch or lot number, the lab that ran it, and the test date. The test date matters more than almost anyone realizes. Hold that thought.
• Cannabinoid potency — THC, THCA, CBD, CBDA, CBG, CBN and friends, each reported as a percentage of weight (flower) or milligrams per gram/serving (edibles, concentrates).
• Terpene profile — the aromatic compounds, usually the top several by percentage. Not every state requires this one, which is part of the problem.
• Safety panels — pesticides, residual solvents, heavy metals, microbials, mycotoxins. You want every line here to read Pass or ND (not detected).

How to read THC: the number is bigger than the label

Here’s the part nobody explains. Raw cannabis flower barely contains any active THC. It containsTHCA — tetrahydrocannabinolic acid — which is not intoxicating until you heat it. When you spark a bowl, hit a vape, or bake it, heat strips a carboxyl group off the molecule and converts THCA into delta-9 THC. Chemists call this decarboxylation.

So a label or COA reports two different things, and they are not interchangeable:

• Delta-9 THC — the active THC already present in the sample, usually a small number on raw flower.
• THCA — the inactive acid that becomes THC when you heat it.

The number that predicts the experience is Total THC — what you actually get once heat does its work. Some COAs print it. Many don’t, which means the math is on you.

The THCA-to-THC math, done once

The formula every lab and regulator uses is:

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

The 0.877 isn’t arbitrary. THCA is a heavier molecule than THC — 358.48 g/mol versus 314.47 g/mol — because of that carboxyl group. When heat knocks the group off (as CO₂), the molecule loses weight. Divide 314.47 by 358.48 and you get 0.877. So a gram of THCA can only ever become 87.7% of a gram of THC. You multiply, you don’t just add.

Worked example. Say a flower COA lists:

• THCA: 28.0%
• Delta-9 THC: 1.2%

Total THC = 1.2 + (28.0 × 0.877) = 1.2 + 24.56 = 25.76%.

Note what just happened. If you read the THCA line and assumed “28% flower,” you overshot the real activated potency by more than two points. If you read only the delta-9 line and thought “1.2%, basically nothing,” you undershot it by a mile. Total THC is the honest middle. Do this on every product and the picture changes fast.

What counts as a good or high number

Percentages mean nothing without a yardstick. Rough, real-world ranges for Total THC:

Terpenes are the other yardstick, and on concentrates they’re the more interesting one. A live resin testing 4–8% total terpenes is loud and full-flavored; under 2% is usually a flatter, more one-note product regardless of how high the THC climbs. On flower, total terpenes above roughly 2% is considered aromatic and well-grown. Higher THC is not the same thing as a better product — the terpene column is where craft shows up.

This is also why chasing the single biggest THC number on the shelf is a beginner’s move. The full profile — cannabinoid ratios plus the terpene lineup — tells you far more about what a session will feel like than one percentage ever will.

Why an old COA overstates what’s left

Go back to that test date. A COA is a snapshot of the product on the day it was tested — not the day you bought it. Cannabinoids are reasonably stable, though THC slowly oxidizes into CBN over months. Terpenes are not stable at all. They’re volatile aromatic compounds, which is a technical way of saying they evaporate. Heat, light, oxygen, and time all drive them off.

So a six-month-old jar tested at 3% terpenes does not still hold 3%. The COA was accurate in the lab and is now optimistic on the shelf. The smell is the giveaway — if the aroma has faded, the terpene numbers on the printout have faded with it, even though the paper still says what it said. When you compare products, weight a recent test date accordingly.

Testing standards differ by state

One COA from California and one from Oklahoma are not necessarily measuring the same way. Required panels, action limits for contaminants, allowed labs, and even whether a terpene profile is mandatory all vary by state. A product that passes in one market might face different thresholds in another, and “tested” means different things depending on where the label was printed. It doesn’t make any single COA wrong — it just means you can’t assume two labels from two states are directly comparable. Always check who the lab is and which state’s rules it’s operating under.

The two-second version

All of the above is worth knowing once. You don’t need to do it by hand every time. That’s the entire reason terptracer.com exists. Scan the COA QR code on the package and TerpTracer decodes the document for you — it runs the Total THC math automatically (delta-9 plus THCA × 0.877), pulls the full cannabinoid and terpene breakdown into a clean profile, and then lets you log how each session actually felt against that data. Over time you stop guessing from a single number on a jar and start reading your own patterns. The data was always there. Now it doesn’t go in the trash.

Frequently asked questions

What does the THC percentage on a cannabis label actually mean?

It depends on which line you’re reading. The big number is often THCA, the inactive acid that becomes THC when heated — not the active THC itself. The number that predicts potency is Total THC, calculated as delta-9 THC plus THCA × 0.877. Reading the THCA line alone overstates activated potency; reading delta-9 alone understates it.

How do you convert THCA to THC?

Use Total THC = delta-9 THC + (THCA × 0.877). The 0.877 factor reflects the molecular weight THCA loses during decarboxylation, when heat removes its carboxyl group as CO₂. For 28% THCA and 1.2% delta-9, Total THC works out to 25.76%.

Why does a COA expire or become less accurate over time?

A COA reflects the product on its test date. Cannabinoids are fairly stable, but terpenes are volatile and evaporate with heat, light, oxygen, and time. An older COA can therefore overstate the terpene content still left in the product, which is why the test date is worth checking before you compare two items.

Are cannabis COAs the same in every state?

No. Required test panels, contaminant action limits, approved labs, and whether terpene testing is mandatory all vary by state. Two COAs from two states aren’t necessarily measuring the same way, so check which lab produced the document and which state’s standards it followed.