Multiply THCA by 0.877 to estimate the THC it can become. That multiplier is the top pick for a THCA to THC conversion chart because it falls straight out of the molecular weights of the two molecules, needs no software, and matches the formula labs print on a certificate of analysis. Three criteria separate a reliable conversion from a sloppy one: whether it adds the delta-9 THC already present in the sample, whether it reflects real decarboxylation efficiency instead of a theoretical ceiling, and whether it matches the THC definition your state uses.
Why the Number Is 0.877
THCA is THC with a carboxyl group attached. Heat breaks that group off and it leaves as carbon dioxide. The THCA molecule weighs 358.47 g/mol and the THC molecule left behind weighs 314.46 g/mol. Divide 314.46 by 358.47 and you get 0.877. The missing 12.3 percent is the CO2 that vents away as vapor.
THCA vs THC: The Legal Difference and What to Buy
The formula on most lab reports is: Total THC = (THCA x 0.877) + delta-9 THC. The second term matters. A sample can carry measurable delta-9 THC before any heat touches it, and leaving that out understates potency.
THCA vs THC Potency Comparison: Which Form Hits Harder?
The THCA to THC Conversion Chart
These figures assume complete decarboxylation. Treat them as a ceiling, not a guaranteed yield.
what is the difference between thca and thc
- 5% THCA becomes 4.4% THC
- 10% THCA becomes 8.8% THC
- 15% THCA becomes 13.2% THC
- 20% THCA becomes 17.5% THC
- 25% THCA becomes 21.9% THC
- 30% THCA becomes 26.3% THC
- 35% THCA becomes 30.7% THC
- 100 mg THCA becomes about 88 mg THC
- 500 mg THCA becomes about 439 mg THC
To add THC that was already there: a sample testing 20% THCA and 0.5% delta-9 THC lands at 18.0% total THC, because 20 x 0.877 = 17.5 and 17.5 + 0.5 = 18.0.
Method 1: Hand Calculation
Take the THCA percentage, multiply by 0.877, then add the delta-9 percentage. For milligrams, do the same with the milligram weight.
Pros
- Works with any calculator and any lab report format
- Nothing to install or subscribe to
- Forces you to look at the actual COA numbers
Cons
- Easy to forget the delta-9 term
- Produces a theoretical maximum, not a realistic edible dose
- Slower when you are comparing dozens of batches
Use this when you are checking a single jar or a single batch and want to confirm the lab did the math right.
Method 2: The Total THC Line on a COA
Most accredited labs print a total THC figure alongside THCA and delta-9. That line is the 0.877 conversion already done for you, with the pre-existing THC folded in.
Pros
- Removes arithmetic errors
- Uses the same method regulators and dispensary labels rely on
- Consistent across brands, so comparison shopping gets easier
Cons
- Not every producer tests for it
- Still a theoretical number if you plan to cook with the flower
- Some reports list THCA and delta-9 without a combined figure
Use this when you are comparing products side by side and want one number per jar.
Method 3: Decarb-Adjusted Estimates for Edibles
Oven decarboxylation rarely hits the theoretical ceiling. Time, temperature, material density, and moisture all pull the yield down, and pushing heat too long starts converting THC into CBN. A working estimate of 70 to 90 percent of the chart value is more useful in a kitchen than the chart itself.
Pros
- Gives a realistic dose per portion instead of a fantasy number
- Accounts for losses from straining and fat absorption
- Safer starting point for anyone new to homemade edibles
Cons
- Requires an assumption, so precision drops
- Home equipment varies too much for one fixed efficiency figure
- No substitute for lab testing your finished oil
Use this when you are infusing butter or oil and need a portion size you can actually repeat.
Where the Chart Overstates Reality
Smoking and vaping decarboxylate on contact, but a share of the THC is destroyed by the heat before it reaches you, so inhaled delivery never matches the raw conversion math. Baked goods lose more, because flour and sugar bind cannabinoids and oven time adds a second round of thermal exposure. Flower stored warm and bright also sheds potency over months as THC oxidizes into CBN, which is why an old jar can test lower than its printed label.
The Legal Line at 0.3 Percent Delta-9
Federal law defines hemp by delta-9 THC concentration of 0.3 percent or less on a dry weight basis. THCA is not part of that federal figure, so a flower can carry 25 percent THCA and still qualify if its delta-9 reading stays under the threshold. Several states calculate total THC instead, which folds THCA in and changes the answer entirely. Check the rule for your state before you assume a number is compliant.
Turning the Chart Into a Dose
- Find the THCA percentage on the COA.
- Multiply by 0.877 and add the delta-9 percentage.
- Multiply that result by your starting weight in milligrams.
- Apply a realistic decarb factor if you are cooking, not smoking.
- Divide by the number of portions, then compare against a 10 mg reference serving.
One gram of 20 percent THCA flower works out to roughly 175 mg of potential THC at full conversion. Split across 12 portions, that is about 14.5 mg each before any decarb losses. The gap between 175 mg and what lands in the brownie is exactly why the chart is a starting point and not a finished answer.