THC percentage is the most prominent number on a cannabis menu, and it's also the most misunderstood. Many shoppers treat it like a quality score: 28% must beat 19%. It doesn't work that way. The number measures one compound in one batch, tested once. It's useful, but it's not the whole story.
Here's what the figure actually measures, how labs calculate it, why it varies, and how Massachusetts labels potency. This guide is for adults 21 and over.
Key takeaways
- THC % is the share of a product's dry weight that is THC, as measured by an independent lab for that batch.
- "Total THC" combines delta-9 THC with the THC that THCA becomes when heated: Δ9-THC + (THCA × 0.877).
- A higher number isn't a quality score. It doesn't measure aroma, freshness or how an experience is described.
- Results vary between batches, samples and labs. A strain name doesn't guarantee a potency.
- Massachusetts labels show potency as a percentage for flower and concentrates, and in milligrams per serving for edibles.
What the percentage actually measures
On flower, pre-rolls and concentrates, potency is shown as a percentage of dry weight. 20% THC means that for every 100 mg of product, about 20 mg is THC. Per gram of flower, that's roughly 200 mg.
In Massachusetts regulations, the Cannabinoid Profile is defined as the dry-weight percentages of four compounds: delta-9 THC, THCA, CBD and CBDA. Labels have to show the full cannabinoid profile. Edible, concentrate, tincture and topical labels also list THC and other cannabinoids per package and per serving, "in absolute terms and as a percentage."
THCA, delta-9 THC and "total THC"
Raw cannabis contains very little delta-9 THC. Most of it is THCA, the acid form. When you apply heat by smoking, vaping or baking, THCA loses part of its molecule (a carboxyl group) and becomes delta-9 THC. That's called decarboxylation.
So a lab report usually shows something like this:
| Cannabinoid | Result |
|---|---|
| Δ9-THC | 0.6% |
| THCA | 23.4% |
| CBD | ND |
| CBDA | 0.1% |
To estimate the THC available after heating, labs commonly use this industry convention. (Massachusetts rules require Δ9-THC and THCA to be reported separately but don't prescribe a Total THC formula.)
Total THC = Δ9-THC + (THCA × 0.877)
The 0.877 factor accounts for the weight lost when THCA converts. In the example above, 0.6 + (23.4 × 0.877) ≈ 21.1% total THC.
This is why you might see "THCA 23%" on one menu and "THC 21%" on another for the same product. They're reporting different lines from the same test. When comparing products, compare total THC to total THC.
Why higher isn't automatically better
It measures one compound. A cannabis flower contains many cannabinoids and aromatic compounds called terpenes. Terpenes shape how a product smells and tastes (see our terpenes guide). THC % tells you none of that.
It says nothing about freshness or handling. A high-testing batch that was stored badly can be dry, harsh and faded by the time you open it. See how to store cannabis.
It isn't a promise about experience. People commonly describe very different experiences from products with similar THC numbers. Potency is one input, not a prediction.
More potent means more caution. A higher percentage means a given amount contains more THC. That's a reason to use less of it, not a reason to reach for it by default. With any product, start low and go slow.
Why THC numbers vary
If you've seen the "same strain" test at 18% one month and 24% the next, here's why.
Batch to batch
A strain name is a genetic label, not a spec. Growing conditions, harvest timing, drying and curing all shift the chemistry. Each production batch is tested on its own, and the label reflects that batch's result.
Sample to sample
Labs test a sample, not the whole batch. The Commission's testing protocol sets rules for taking representative samples. Even so, cannabinoids aren't perfectly even across every bud. Top flowers and lower flowers can test differently.
Moisture
Because results are reported by weight, water content matters. The same flower tested wetter or drier can show a slightly different percentage.
Lab methods
Labs follow the state's protocol and accreditation requirements, but equipment, preparation and calibration still differ. That's one reason Massachusetts requires testing by independent, licensed labs. It's also why the regulations call for a second confirmatory test at a different lab when a failed product is reanalyzed.
The official variance
For edibles, Massachusetts writes a tolerance directly into the rules. Single servings tested for potency are subject to a variance of no more than ±10% (935 CMR 500.160(12)). That's why the edible limits read 5.5 mg per serving and 110 mg per package: a 5 mg nominal serving and a 100 mg nominal package, plus the 10% variance.
Potency in concentrates and vapes
Concentrates and vape oils are refined to concentrate cannabinoids, so their percentages are typically far higher than flower's. That's a difference in form, not a sign that one is "better." A small amount of a concentrate can contain as much THC as a much larger amount of flower. Compare concentrates with concentrates, and be more careful with anything more concentrated. For how these products are made, see live resin vs. live rosin vs. distillate, and browse the concentrates menu to compare lab summaries.
How Massachusetts labels potency
| Product type | How potency appears |
|---|---|
| Flower & pre-rolls | Full cannabinoid profile (THC and other cannabinoids), as percentages |
| Concentrates & vapes | Cannabinoid profile per package and per serving (if applicable), in absolute terms and as a percentage, plus additives such as terpenes |
| Edibles | THC and other cannabinoids per serving and per package, in mg; number of servings; serving size in mg |
| Tinctures & topicals | THC and other cannabinoids per package and per serving (if applicable) |
Every label also has to carry a statement and seal that the product was tested for contaminants with no adverse findings, and the date of testing.
Edible serving rules are covered in detail in our edibles guide for first-timers.
How to use THC % when you shop
- Compare like with like. Total THC to total THC, flower to flower. A 75% vape oil and a 20% flower aren't on the same scale.
- Look at the rest of the profile. Is there measurable CBD? Are terpenes listed?
- Check the test date. Massachusetts results are valid for one year.
- Match the batch. The number applies to the batch that was tested. See how to read a certificate of analysis.
- Treat higher numbers as a reason to go slower.
On our product pages, potency comes from the lab summary tied to the package's METRC tag when it's available. It doesn't come from a brand's marketing copy. Our lab results page explains every field, and the METRC package tag explained covers where the data comes from.
Compare real numbers: browse flower, pre-rolls or vapes and open the lab summary on any product. Delivery covers Boston, Brookline, Waltham and the rest of our service area. Adults 21+ only.
For use only by adults 21 years of age or older. Keep out of the reach of children. This article is general information, not medical advice.
Frequently asked questions
What does the THC percentage on flower mean?
It's the share of the product's dry weight that is THC, as measured by an independent lab. A flower labeled 20% total THC contains about 200 mg of potential THC per gram.
What's the difference between THCA and THC?
THCA is the acid form found in raw cannabis. Heat converts it to delta-9 THC. Labs report both, and many also calculate total THC as delta-9 THC plus THCA multiplied by 0.877.
Is higher THC better?
Not necessarily. THC percentage measures one compound. It doesn't measure quality, freshness, aroma or how an experience is commonly described. Higher potency also means a given amount contains more THC, which calls for more caution, not less.
Why might two labs report different THC numbers for the same strain?
Different batches, different samples from the same batch, moisture content, sample preparation and lab methods can all shift results. A strain name doesn't fix a THC number. Each batch is tested on its own.
How is potency shown on Massachusetts edibles?
In milligrams, per serving and per package. Massachusetts caps an edible serving at 5 mg of THC and a package at 100 mg, with a 10% testing variance written into the limits (5.5 mg and 110 mg).
Sources
- 935 CMR 500.000: Adult Use of Marijuana (effective 06/18/26), Cannabis Control Commission · masscannabiscontrol.com
- 935 CMR 500.105: Labeling requirements (Cornell LII) · law.cornell.edu
- 935 CMR 500.150: Edible Marijuana Products (Cornell LII) · law.cornell.edu
- Protocol for the Sampling and Analysis of Finished Marijuana Products, Cannabis Control Commission (rev. Dec. 30, 2021) · masscannabiscontrol.com
Rules change. We check official sources when we update a post; confirm current requirements with the Cannabis Control Commission before relying on them.