You open two cannabis lab reports, find the same row, and spot two different numbers. Both have decimal places. Both look official. So which one should you trust?
Before choosing a winner, check what the numbers describe. Different samples, testing methods, and reporting conventions can all affect the comparison. Even a carefully measured result comes with some uncertainty. That deserves an explanation.
Here is how to make sense of the gap without needing to become a laboratory analyst.
Start with what was actually tested
A familiar product name is only the beginning. Are the reports for the same batch, or different batches sold under the same name? Do the sample descriptions match? Are you looking at flower on both reports?
If the batch or material differs, you are comparing different starting points. You cannot isolate the lab's contribution from the two headline numbers alone. Our guide to reading a certificate of analysis explains where to find the identifying details.
Sample preparation matters, too. In its cannabis laboratory comparison work, the National Institute of Standards and Technology (NIST) carefully blended study materials and checked their consistency across packets. That work helps separate differences in the material sent to each lab from differences in the measurements. NIST cannabinoid study, 2024
For a reader, the useful question is simple: were these comparable samples? A matching product name cannot answer that by itself.
The route to the number matters
A lab result involves more than placing a sample in a machine. Preparing the sample, separating compounds, identifying them, and checking the instrument against reference standards all contribute to the measurement.
NIST's Cannabis Laboratory Quality Assurance Program examined differences associated with sample preparation and analytical methods. Its 2024 cannabinoid report also identified calibration and interference from other compounds as potential sources of disagreement. These are specific things laboratories can investigate when results disagree. NIST program overview and cannabinoid report
The report studied particular materials and participating laboratories. It does not tell us why any two retail reports differ, and it does not establish a single acceptable gap for every cannabinoid, concentration, or product.
Check the fine print beside the percentage
Two percentage signs can hide an important difference: what weight is the calculation based on?
An “as received” result describes the material with its moisture included. A result on a dry-weight basis accounts for that moisture. With a different amount of material in the denominator, the same cannabinoid amount can produce a different percentage. NIST identifies moisture measurement as important for reporting cannabis results on a dry-weight basis. NIST reference-material overview
Moisture measurement can introduce differences of its own. In a study published in 2022, NIST sent one hemp material to participating laboratories and found a wide range of reported moisture loss across drying methods. Its findings describe a laboratory comparison using one material. NIST moisture study
Also check that you are comparing the same row and units. THCa, delta-9 THC, and total THC are different entries. Our THCa percentage guide covers those distinctions. If either report leaves the reporting basis unclear, ask the issuing lab before treating the percentages as directly comparable.
Look beyond the decimal places
“Measurement uncertainty” sounds less reassuring than it should. It describes how well a measurement is known, given the information available. It is part of interpreting a result responsibly. NIST explanation of measurement uncertainty
An uncertainty estimate gives context to the reported value. Its meaning depends on how it was calculated and expressed, so a plus-or-minus figure needs an explanation of its own. Simply counting decimal places will not tell you whether two results meaningfully disagree.
NIST's hemp reference material illustrates the point. It comes with assigned values and uncertainty estimates that labs can use to check their methods. Even a carefully characterized reference has uncertainty attached. NIST reference material
Ask for the explanation that fits these reports
If the difference still leaves you wondering, send the brand or issuing laboratory both complete reports. Point to the exact row and ask:
- Do these reports describe the same batch and comparable samples?
- Are the units and reporting basis the same?
- Could the methods or measurement uncertainty explain this difference?
Those questions give someone a specific comparison to investigate. A difference alone does not establish misconduct, and “lab results vary” is not a complete explanation of a particular discrepancy. Keep the report IDs with your question so the reply can address the actual records in front of you.