When you buy cannabis at a store, the potency number on the label is your main guide, but it is not a complete measure. Ask for the Certificate of Analysis (COA) and check the total THC, which includes THCA converted to THC. The most reliable potency measurement comes from a third-party lab using high-performance liquid chromatography (HPLC) or gas chromatography (GC).
What Potency Actually Means
Potency refers to the concentration of active cannabinoids, mainly delta-9-tetrahydrocannabinol (THC) and cannabidiol (CBD). For flower, potency is expressed as a percentage of dry weight. For edibles, it is listed as milligrams per serving. For concentrates, it is often a percentage.
Total THC vs Raw THC
Raw THC (delta-9-THC) is what is already active. THCA is the acidic form that becomes THC when heated (decarboxylation). Total THC is calculated as delta-9-THC plus 0.877 times THCA. Always look for total THC on the label.
CBD and Minor Cannabinoids
CBD potency is measured the same way, often as total CBD (CBD plus 0.877 times CBDA). Minor cannabinoids like CBG, CBN, and CBC also appear on lab reports. They can affect the overall experience.
How Labs Measure Cannabinoids
Labs follow a set process. First, they take a representative sample from a batch. Then they extract cannabinoids with a solvent. Next, they analyze the extract.
Decarboxylation and Calculation
For products that will be heated, labs may decarboxylate the sample to measure total THC. For raw flower, they measure both THCA and THC. The conversion factor is 0.877.
Analytical Methods
HPLC is common for measuring acidic and neutral cannabinoids in one run. GC requires heat, which decarboxylates THCA, so it measures total THC. Both methods are valid, but they can give different numbers.
Reading a Certificate of Analysis
A COA lists cannabinoid percentages, terpenes, moisture, and sometimes pesticides and heavy metals. Check the batch number and test date. Look for total THC and total CBD.
What to Look For at the Dispensary
- Total THC percentage, not just delta-9-THC.
- Total CBD and ratio of THC to CBD.
- Lab name and accreditation.
- Batch date and harvest date.
- Terpene profile if available.
- Whether the product is flower, concentrate, or edible, because potency is expressed differently.
Parameter Bands for Common Products
These ranges are typical for legal markets, but they vary by state and product type.
- Flower: 15% to 25% total THC.
- Vape cartridges and concentrates: 60% to 90% total THC.
- Edibles: 5 mg to 10 mg THC per serving.
- Tinctures: 5 mg to 20 mg THC per milliliter.
- Topicals: low THC, often under 5 mg per dose, with more CBD.
Common Pitfalls
- Trusting only the delta-9-THC number and ignoring THCA.
- Assuming a higher potency always means a better high. Terpenes and other cannabinoids matter.
- Comparing lab results from different labs without checking their methods.
- Forgetting that edible potency is per serving, and a package may contain many servings.
- Ignoring the batch date, because potency can degrade over time.
FAQ
Can I measure cannabis potency at home?
Home test kits can give a rough estimate, but they are not as accurate as lab HPLC or GC. For precise potency, rely on a third-party lab report.
Why do two labs report different THC percentages for the same product?
Sampling differences, extraction methods, and calculation choices (like the decarboxylation factor) can cause variation. A 10% to 20% difference is not unusual.
Does a higher THC percentage mean a stronger effect?
Not always. THC is the main psychoactive compound, but terpenes and other cannabinoids can change the experience. A 20% THC flower with high myrcene may feel different from a 25% flower with low terpenes.
What is the most accurate way to measure potency?
A third-party lab using HPLC with a standard curve and quality controls is the most accurate method available to consumers.