Total THC formula:
Total THC = (THCA × 0.877) + Delta-9 THC
Three variables. Two come from your Certificate of Analysis. One is a constant.
THCA is the dominant cannabinoid in raw cannabis flower. On a Certificate of Analysis it shows up as a percentage by dry weight, usually somewhere between 18% and 30% for commercial flower.
Delta-9 THC is the trace amount of already-decarbed THC in the raw flower. Federal hemp law caps this at 0.3% by dry weight at harvest. On a COA, this number is usually under 0.3% for legal hemp products.
0.877 is the mass-conversion factor. When THCA decarboxylates (loses its carboxyl group when heated), the molecule sheds about 12.3% of its mass as CO2 and water. The remaining 87.7% is what becomes Delta-9 THC. We derive this number in the next section.
This formula matters for four reasons: federal hemp compliance, drug test exposure estimation, real high prediction, dose calibration. Each application uses the same calculation. Each cares about a slightly different decimal.
How to Calculate Total THC Step by Step (Worked Example)
Worked calculation using a realistic Passion Farms COA. Sample numbers: 24.7% THCA, 0.21% Delta-9 THC.
Step 1, Find Your THCA Percentage
On the COA, locate the cannabinoid panel. THCA is usually listed first or second. Number is a percentage by dry weight.
For this example: THCA = 24.7%
Step 2, Multiply by 0.877
Multiply the THCA percentage by 0.877.
24.7% × 0.877 = 21.66%
This number represents the Delta-9 THC equivalent of the THCA after full decarboxylation. It’s the active THC that would result if all the THCA converted perfectly.
Step 3, Add the Delta-9 Reading
Find the Delta-9 THC line on the COA (usually right under THCA in the cannabinoid panel). Add it to the result from Step 2.
21.66% + 0.21% = 21.87%
That’s your Total THC percentage by dry weight.
Step 4, Convert to Milligrams (Optional)
Want to know how many milligrams of Total THC are in a specific product? Multiply the percentage by the product weight in milligrams.
For a 1g (1000mg) pre-roll:
1000 mg × 21.87% = 218.7 mg Total THC
For a 3.5g (3500mg) eighth:
3500 mg × 21.87% = 765.5 mg Total THC
Worked Example Table
| Step | Input | Operation | Result |
| 1 | THCA from COA | Locate percentage | 24.7% |
| 2 | THCA × 0.877 | Multiply | 21.66% |
| 3 | + Delta-9 THC | Add | 21.66% + 0.21% |
| 4 | Total THC | Final | 21.87% |
For our 1g sample: 218.7 mg of equivalent Total THC.
That’s the entire process. Two numbers from the COA, one multiplication, one addition. Whole calculation takes 30 seconds with a phone calculator.
Why 0.877? (The Molecular Weight Math)
The 0.877 isn’t an arbitrary constant. It’s a mass-ratio derived from the molecular weights of two cannabinoids.
THCA molecular weight: 358.47 grams per mole (g/mol). The mass of one mole of pure THCA molecules.
Delta-9 THC molecular weight: 314.46 g/mol.
When THCA decarboxylates, the molecule loses a single CO2 (carbon dioxide) group. That CO2 has a molecular weight of 44.01 g/mol. So:
358.47 (THCA) – 44.01 (CO2 lost) = 314.46 (Delta-9 THC)
Math checks. THCA minus CO2 equals Delta-9 THC. The mass that remains after decarboxylation, expressed as a fraction of the starting mass:
314.46 / 358.47 = 0.8771
Rounded to three decimal places: 0.877. That’s the multiplier.
So if you start with 1.000 gram of pure THCA and decarboxylate it perfectly, you end up with 0.877 grams of pure Delta-9 THC plus 0.123 grams of CO2 and water that left the molecule as gas.
The Decarboxylation Equation
In chemistry notation:
THCA (C22H30O4) → Delta-9 THC (C21H30O2) + CO2
One THCA molecule becomes one Delta-9 THC molecule plus one CO2 molecule. The hydrogen and oxygen counts work out. Carbon count drops by one (the carboxyl carbon leaves as CO2). Same decarboxylation reaction every cannabis consumer triggers every time they light a joint, hit a vape, or bake a brownie with cannabis butter.
Where the 44 g/mol CO2 Goes
The CO2 doesn’t enter your bloodstream. Escapes as gas during heating. In a joint, you might see a slight puff of CO2 leaving the cherry as the flower combusts. In an oven decarb (used for edibles), the CO2 vents off as the flower heats up over 30 to 45 minutes at around 220°F. Either way, that mass is gone from the consumed cannabinoid total.
Why Some Sources Use 0.88 (Rounded)
You’ll occasionally see the multiplier given as 0.88 instead of 0.877. The 0.88 version is rounded to two decimal places. For most practical purposes the difference is trivial: a 25% THCA flower calculated at 0.88 gives 22.00% versus 21.93% at 0.877. The 0.07 percentage point gap doesn’t matter for buying decisions. It does matter for regulatory math at scale (a 1000-pound batch of hemp has a 70-gram difference in calculated Total THC between the two multipliers, which can decide federal compliance).
Federal regulators use 0.877. Most COAs report calculations to two or three decimal places. We use 0.877 throughout this piece.
How to Read a Cannabis COA (Applied Use)
A Certificate of Analysis (COA) is a third-party lab report on a specific batch of cannabis. Every reputable brand publishes one. You access it through a QR code on the package or a link on the product page. Reading order matters.
The Cannabinoid Panel (What to Look For)
Panel lists each cannabinoid the lab tested for, in percentage by dry weight. Key fields:
- THCA (tetrahydrocannabinolic acid), the acid form, dominant in raw flower
- Delta-9 THC, the active form, trace amount in legal hemp
- CBD and CBDA, cannabidiol and its acid form
- CBG, CBGA, cannabigerol and its acid form
- CBN, cannabinol, a degradation product
- Total Cannabinoids, sum of all detected cannabinoids
- Total THC, sometimes pre-calculated by the lab using the 0.877 formula
“Total THC” is shown? You can either trust it or verify with the formula. Not shown? Calculate it yourself using the THCA and Delta-9 numbers.
How to Verify a Brand’s Total THC Claim
Take the brand’s stated Total THC. Calculate it yourself from the THCA and Delta-9 numbers on the COA. The two numbers should match within a tenth of a percent. Brand’s claim is significantly higher than your calculation? They may be using “Total Cannabinoids” mislabeled as “Total THC”, which is a marketing inflation tactic.
Example check:
- Brand claims: 28.4% Total THC
- COA reads: 31.2% THCA, 0.18% Delta-9 THC
- Your calculation: (31.2 × 0.877) + 0.18 = 27.36% + 0.18% = 27.54% Total THC
Brand’s claim of 28.4% is 0.86 percentage points too high. Probably they used 0.88 rounded plus generous rounding. Or they’re claiming closer to Total Cannabinoids. Either way, your number is the verifiable one.
Red Flags on a COA
- No third-party lab name. COA must be from an ISO-accredited lab independent of the brand.
- Old batch date. COAs over a year old don’t reflect current product.
- No residual solvent panel. Concentrate COAs should test for hydrocarbon residuals.
- No heavy metals / pesticide panel. A real lab tests these.
- Inconsistent THCA-to-Total-THC math. Can’t reconcile the brand’s stated Total THC with the 0.877 formula? Something is off.
Total THC vs Total Cannabinoids (They’re Different)
Two numbers that sound similar. Two very different meanings.
Total Cannabinoids is the sum of every detected cannabinoid in the COA, in their acid and active forms, including the ones that aren’t psychoactive. So Total Cannabinoids = THCA + Delta-9 THC + CBD + CBDA + CBG + CBGA + CBN + and so on. The number is usually 1% to 5% higher than Total THC because it adds in the non-THC compounds.
Total THC is only the active and convertible THC. The formula: (THCA × 0.877) + Delta-9 THC. CBD and CBG don’t contribute. The number represents the actual THC potency after decarboxylation.
Why this matters: brands sometimes report “Total Cannabinoids” as a headline number because it looks bigger. A flower with 28% Total Cannabinoids might have 22% Total THC and 4% CBD and 2% CBG. The 28% number is technically accurate. It just doesn’t represent the THC content. Confusing the two leads buyers to overestimate potency.
For dose calculation, drug-test estimation, federal compliance, or real-high prediction: use Total THC. For “what’s the chemical profile of this flower” overall: use Total Cannabinoids.
Why This Number Matters (Real Application)
Five places the Total THC number gets used.
For Drug Test Estimation
Total THC correlates with THC metabolites your body produces and excretes. The metabolites are what drug tests detect. A 25% Total THC pre-roll smoked daily for a week will produce metabolite levels that test positive on standard urine screens for 2 to 4 weeks after the last consumption. A 15% Total THC casual flower might clear in 1 to 3 weeks for the same usage pattern.
Math isn’t linear (body fat, metabolism, hydration all matter), but Total THC is the variable that scales the exposure. Calculating it accurately lets you estimate detection windows.
For Tolerance Calibration
You smoked 22% Total THC flower yesterday and you switching to 28% Total THC flower today? Dose should drop by roughly 22 / 28 = 0.79. So a half-gram session yesterday becomes a 0.4-gram session today for equivalent exposure. Total THC number is what you use to do that math.
For Comparing Flower to Concentrate
A 25% Total THC flower delivers 250 mg of equivalent THC per gram of dry weight (1000mg × 25%). A 90% Total THC concentrate (like Drip Diamonds) delivers 900 mg per gram. So 0.1g of the concentrate equals 0.36g of the flower in active THC. Cross-product math depends entirely on Total THC.
For our flower catalog, every product COA shows the Total THC calculation so you can do this math directly.
Federal vs State Total THC Rules (The Legal Layer)
The 2018 Farm Bill defined hemp as Cannabis sativa with no more than 0.3% Delta-9 THC by dry weight at harvest. Bill is clear that the test is Delta-9, not Total THC.
But state-level interpretations vary. Some states accept the federal Delta-9-only threshold. Others apply the Total THC formula to determine hemp status, which is a much stricter standard.
State Application Matrix (as of 2026-05-12, verify before publish)
| State | Hemp Threshold Interpretation | Total THC Rule |
| Federal (2018 Farm Bill) | 0.3% Delta-9 THC at harvest | Delta-9 only |
| Texas | 0.3% Delta-9 THC | Delta-9 only (SB 3 under review) |
| North Carolina | 0.3% Delta-9 THC (until Nov 2026) | Delta-9 currently, restriction coming |
| California | 0.3% Total THC (post-AB 45) | Total THC formula applied |
| Florida | 0.3% Total THC | Total THC formula applied |
| Colorado | 0.3% Delta-9 THC | Delta-9 only |
| Oregon | 0.3% Delta-9 THC | Delta-9 only |
| Michigan | 0.3% Total THC | Total THC formula applied |
State uses Total THC? A flower at 25% THCA + 0.15% Delta-9 calculates to 22.08% Total THC, which is 73x over the 0.3% threshold. Federal-compliant hemp under the Delta-9 rule. Non-compliant under Total THC rules.
This is the legal fault line for hemp-derived THCA products. North Carolina’s SB 328 takes effect November 12, 2026 and tightens the state’s interpretation. Several other states are considering similar measures.
Federal Interpretation (Delta-9 Only)
USDA Final Rule on hemp production specifies the Delta-9 measurement. The DEA, despite occasional internal directives suggesting otherwise, has not formally adopted Total THC at the federal level. Hemp-derived THCA products remain federally legal as of the 2026 publication date, contingent on Delta-9 staying under 0.3% at harvest.
Why the Formula Matters Even in Delta-9-Only States
Even in states using the federal Delta-9-only rule, Total THC matters for product labeling, dose calculation, and consumer protection. A brand selling a “28% THCA flower” without disclosing Total THC is technically compliant but informationally vague. Honest brands publish Total THC because that’s what buyers care about for their actual high.
The Limits of the 0.877 Formula (Honest Disclosure)
The formula assumes 100% decarboxylation efficiency. Real-world combustion doesn’t hit 100%.
Real Decarboxylation Efficiency (70-90% Range)
Different consumption methods produce different efficiency rates:
| Method | Decarb Efficiency Range | Real Total THC (from 25% THCA) |
| Combustion (joint, bowl) | 70-85% | 17.5% to 21.3% |
| Vaporization (dry herb) | 80-90% | 20.0% to 22.5% |
| Dab rig (concentrate) | 90-95% | 22.5% to 23.8% |
| Oven decarb (edible prep) | 85-95% | 21.3% to 23.8% |
| Theoretical (formula) | 100% | 21.87% |
Smoke a 25% THCA flower? Formula says you consuming 21.87% Total THC equivalent. Real bloodstream terms? Closer to 18% to 21% depending on your technique, the device, and how much THC degrades to CBN during combustion.
This doesn’t make the formula wrong. Makes the formula a legal and labeling standard, not a perfect bloodstream-exposure predictor.
Why the Formula Still Matters Anyway
The 0.877 multiplier is the regulatory standard. The labeling standard. The COA reporting standard. The cross-product comparison standard. Every brand uses it. Every lab uses it. Every state law applying Total THC uses it. The number doesn’t predict your individual high. The number does predict whether the product is legal, how it compares to other products, and what your typical exposure looks like.
When we publish a COA at Passion Farms, the Total THC number we list is calculated with 0.877. Number you’d calculate yourself with the same THCA and Delta-9 readings will match ours. That’s the entire point of the formula: it’s reproducible.
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Formula is (THCA × 0.877) + Delta-9 THC. The molecule loses 12.3% of its mass during decarboxylation. The 0.877 is that mass-loss fraction.
Passion Farms publishes Total THC on every COA in the flower category. We don’t hide behind “total cannabinoids” marketing math. The number we show is the number you calculate yourself from the THCA and Delta-9 readings on the same COA.
Send this page to anyone who asks “how strong is THCA flower really.” The math is the math. The chemistry is the chemistry. The label is the label.
FAQ
What is the total THC formula?
Total THC = (THCA × 0.877) + Delta-9 THC. THCA and Delta-9 come from a Certificate of Analysis as percentages by dry weight. 0.877 is the molecular mass-loss factor when THCA decarboxylates to Delta-9 THC.
Why is the multiplier 0.877?
It’s the molecular weight ratio. THCA weighs 358.47 g/mol. Delta-9 THC weighs 314.46 g/mol. When THCA decarboxylates, it loses a CO2 molecule (44.01 g/mol). The ratio 314.46 / 358.47 = 0.8771, rounded to 0.877.
How do I calculate total THC from THCA?
Take the THCA percentage from the COA. Multiply by 0.877. Add the Delta-9 THC percentage from the same COA. The sum is your Total THC. For a flower at 25% THCA and 0.2% Delta-9: (25 × 0.877) + 0.2 = 22.13% Total THC.
What’s the difference between total THC and total cannabinoids?
Total THC is the active THC content after decarboxylation, calculated with the 0.877 formula. Total Cannabinoids is the sum of all cannabinoids (including CBD, CBG, CBN). Total Cannabinoids is usually 1-5% higher than Total THC.
Is total THC the same as THCA?
No. THCA is the acid form before decarboxylation. Total THC is the calculated active THC equivalent after decarboxylation. Total THC will always be lower than THCA by about 12.3% (because decarboxylation loses mass as CO2).
How do I read total THC on a COA?
Look for a “Total THC” line item. Present? The lab pre-calculated it. Not? Find the THCA and Delta-9 percentages and apply the formula yourself: (THCA × 0.877) + Delta-9 = Total THC.
Does the formula work for edibles?
Yes for pre-decarbed edibles (gummies, chocolates, baked goods where the cannabis was decarbed before use). The active ingredient is already Delta-9 THC. For raw cannabis edibles (rare), you’d need to apply the formula to estimate active THC after consumption-related conversion.
Do state laws use total THC or just Delta-9?
It varies. The federal 2018 Farm Bill uses Delta-9 only. Some states (California, Florida, Michigan) apply the Total THC formula for legal hemp definition, making the threshold much stricter. Most states still use the federal Delta-9-only standard.
Is 25% THCA the same as 25% total THC?
No. 25% THCA converts to roughly 21.93% Total THC after applying the 0.877 multiplier and assuming a typical 0.2% Delta-9 baseline. The two numbers always differ by approximately 12% in relative terms.
How accurate is the 0.877 formula?
The molecular math is exact. Real-world decarboxylation efficiency is not 100%. Combustion achieves 70-85%, vaporization 80-90%, dabbing 90-95%. The formula gives the maximum theoretical Total THC. Real bloodstream exposure is typically 5-15% lower than the formula predicts.
What does total THC mean for drug testing?
Total THC scales with the metabolite levels detectable on drug tests. Higher Total THC products produce higher metabolite levels per gram consumed, leading to longer detection windows. The formula doesn’t directly tell you whether you’ll fail a test, but it scales the exposure proportionally.
Can total THC be lower than THCA?
Yes, almost always. Total THC = THCA × 0.877 + Delta-9. Unless Delta-9 is very high (over 12% of THCA, which only happens in fully decarbed products), Total THC will be lower than THCA on every standard COA.
