PLENNY LEARN · UNDERSTANDING LAB NUMBERS
Same sample. Different denominator.
Dry-weight potency excludes moisture from the sample weight used to calculate a concentration. As-received potency includes the moisture present in the tested sample. That difference can make the dry-weight percentage higher, even when both numbers describe the same amount of a cannabinoid.
By Plenny · Updated September 18, 2026 · 4 minute read
What does dry weight mean on a cannabis COA?
Think of a percentage as an amount divided by a reference weight. The reporting basis tells you which weight the laboratory used. “Dry weight” is a calculation basis, not a description of how dry the product feels.
The reference weight includes moisture in the sample. Look for this phrase in the report’s notes or column headings.
The reference weight excludes moisture. A smaller denominator can produce a larger concentration percentage.
Compare like with like. THCA, delta-9 THC and total THC are different report entries, regardless of the weight basis.
USDA’s hemp laboratory guidance defines dry-weight reporting as excluding moisture and describes moisture correction as one way a laboratory can report that result. This guidance concerns hemp-production testing; it is not a rule for every retail COA.
Why 18% and 20% can describe the same sample
This is an invented arithmetic example, not a real product report. Assume a 1.00 g sample contains 0.18 g of a measured cannabinoid and 0.10 g of water. Its dry matter weighs 0.90 g.
Show the as-received percentage
0.18 ÷ 1.00 × 100 = 18%
The denominator is the full sample weight, including water.
Show the dry-weight percentage
0.18 ÷ 0.90 × 100 = 20%
The denominator excludes the water. The example still contains the same 0.18 g of the measured cannabinoid.
Did the calculation create more cannabinoid?
No. It changed the reference weight used to express concentration. A higher dry-weight number alone does not show that a sample contains more cannabinoid than another sample.
For moisture expressed as a percentage of the original, as-received mass, the relationship is:
Dry-weight % = as-received % ÷ (1 − moisture % ÷ 100)
Sikora and colleagues’ study in the Journal of AOAC INTERNATIONAL explains the distinction between moisture on wet- and dry-weight bases. Confirm the moisture convention before using a conversion. Do not correct a result that the laboratory has already reported on a dry-weight basis.
How to compare potency on two COAs
Start with the compound name, units and reporting basis. “20% THCA, dry weight” and “18% total THC, as received” differ in more than one way. Comparing just the two numbers leaves out important information.
Then check that the report identifies the intended batch and sample type. A result for flower is not interchangeable with a result for an extract or finished edible. Sampling, analytical methods and measurement uncertainty also matter; matching the weight basis does not remove every source of difference.
SC Labs’ COA walkthrough shows where sample identifiers, product types, methods and detailed results appear. Those fields help you establish what each number actually describes.
If the basis is missing, ask the laboratory: “Is this result as received or moisture-corrected, and which moisture measurement and definition were used?” Do not guess from the percentage alone.
Why reports may use different conventions
The purpose of the test and the applicable reporting requirements can differ. USDA hemp-production guidance calls for dry-weight total THC reporting. By contrast, a March 2024 Massachusetts Cannabis Control Commission letter directed its laboratories to report cannabinoids as received for the product categories it addresses.
These documents illustrate why the report’s context matters. They are not interchangeable instructions for every laboratory or jurisdiction. Use current requirements for the particular program when evaluating compliance.
Neither phrase is a quality grade. A dry-weight result does not, by itself, prove fraud, better quality or stronger effects. An as-received result does not, by itself, prove that every required safety test was performed.
Before comparing the percentages
This checklist helps identify missing context. It does not independently verify a laboratory result or determine whether a product meets a legal threshold.
Common questions
Does “wet weight” mean the flower is fresh or uncured?
Not necessarily. In a concentration calculation, wet-weight or as-received basis includes the sample’s moisture. Even dried plant material can retain moisture. Read the laboratory’s definition.
Can I use water activity as the moisture percentage?
No. Water activity and moisture content are different measurements. An Aw value is not the percentage of water by mass and cannot be substituted into this example’s equation.
Is dry-weight correction the same as calculating total THC?
No. Moisture correction changes the weight basis. A total THC calculation combines specified cannabinoid results using the relevant conversion factor. Identify both the cannabinoid calculation and the weight basis on the report.
Keep learning
Sources and scope
Sources checked September 18, 2026. The worked example holds cannabinoid mass constant to explain reporting arithmetic. It does not model physical drying, predict effects or establish product legality. Consult the laboratory for its reporting conventions and the relevant regulator for current requirements.
Chris Garcia, Owner and CEO
September 18, 2026
How this page is prepared: Plenny uses linked research and other relevant sources for educational explanations, and product details and batch COAs where relevant. General strain, flavor, and effect descriptions are not guarantees.
Commercial transparency: Plenny sells products discussed on this website. Educational pages are not medical or legal advice, and content is not medically reviewed unless a named licensed reviewer is shown.