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How to Read THCA and THC on a Label and Calculate Total Potency
Learn to calculate total THC from THCA using the standard formula. Convert percentages to mg, read COAs correctly, and understand why your math doesn't match reality.
Written by Lorien Strydom
December 1st, 2025
Labels show THCA and THC separately, which confuses everyone trying to understand actual potency. You'll learn to read any COA, do the math correctly, convert to practical milligrams, and understand why your experience differs from theoretical calculations.
Table of Contents
Why THCA and THC Show Up Separately on Labels
The Standard Formula for Total THC
How to Read THCA and THC on a Certificate of Analysis
Converting Percentages into Milligrams You Can Actually Use
Why Your Experience Feels Different from the Math
What Different Product Types Mean for Your Calculations
How Lab Testing Methods Change What You See
The Legal Context Behind THCA and Total THC
Why THCA and THC Show Up Separately on Labels
THCA is the non-intoxicating form in raw flower that becomes more potent when heated. When you smoke, vape, or cook cannabis flower, that heat transforms THCA into the familiar effects you expect.
THC on labels means already-active Δ9-THC, which is usually minimal in raw flower.
Most high-quality THCA flower shows percentages like 25% THCA with only 0.2-0.3% Δ9-THC.
Is 30% THCA the Same as 30% THC?
No, 30% THCA converts to approximately 26.3% THC when heated due to molecular weight loss during the conversion process. The THCA molecule sheds a carboxyl group when exposed to heat, reducing its weight by about 12.3%.
The Standard Formula for Total THC
The industry-standard formula for calculating total potential THC is straightforward: Total THC = (THCA × 0.877) + Δ9-THC.
The 0.877 factor accounts for molecular weight adjustment. When THCA loses its carboxyl group during heating, it becomes lighter—specifically, it retains 87.7% of its original weight as THC.
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How to Convert THCA Percentage to THC?
Multiply THCA percentage by 0.877 and add any existing THC percentage to get total potential THC after heating. The USDA uses this formula for hemp testing compliance and by state cannabis control commissions across the country.
How Do You Calculate Total THC?
Use the formula Total THC = (THCA × 0.877) + Δ9-THC, where 0.877 accounts for the molecular weight change when THCA loses its carboxyl group. Here are two practical examples:
Example 1: A cannabis strain shows 20% THCA and 0.2% Δ9-THC on its COA.
Multiply THCA by 0.877: 20 × 0.877 = 17.54
Add the existing Δ9-THC: 17.54 + 0.2 = 17.74% total THC
Example 2: A premium flower tests at 25% THCA and 0.3% Δ9-THC.
Multiply THCA by 0.877: 25 × 0.877 = 21.93
Add the existing Δ9-THC: 21.93 + 0.3 = 22.23% total THC
This calculation reveals why high-THCA hemp flower delivers effects comparable to traditional cannabis despite showing tiny Δ9-THC numbers on the label.
How to Read THCA and THC on a Certificate of Analysis
Every reputable hemp product comes with a Certificate of Analysis (COA) from a third-party laboratory. The Potency section is where you'll find the cannabinoid percentages you need for your calculations.
We use HPLC testing through Marin Analytics, which keeps THCA and Δ9-THC values separate. Look for a table showing cannabinoid names in one column and percentages in another.
You'll see THCA listed with its percentage—commonly 15-30% for potent flower. Below that, you'll find Δ9-THC, usually showing 0.1-0.3% for compliant hemp products.
These are the only two numbers you need for the total THC calculation.
HPLC testing reports acids and neutrals separately, providing clean data for accurate calculations. This method doesn't apply heat during analysis, so what you see on the COA reflects the raw plant chemistry before consumption.
Converting Percentages into Milligrams You Can Actually Use
Percentages tell you concentration, but milligrams tell you how much THC you're actually consuming.
The conversion is simple: multiply the THC percentage by 10 to get milligrams per gram, then multiply by your product weight.
How Much THC is in a Gram of Flower?
A gram of 20% total THC flower contains 200mg of potential THC. Here's how that breaks down across common consumption amounts:
0.1g (one-tenth of a gram): 20% × 10 = 200mg per gram, multiplied by 0.1g = 20mg of total THC.
0.5g (half gram): 200mg per gram, multiplied by 0.5g = 100mg of total THC. This is a typical amount for a pre-roll joint.
1g (full gram): 200mg per gram, multiplied by 1g = 200mg of total THC. This is the standard measurement for flower purchases.
These numbers represent potential THC after complete heating—but as we'll discuss next, real-world consumption delivers significantly less than these theoretical maximums.
Why Your Experience Feels Different from the Math
Educational Note: The following information represents scientific findings about cannabinoid chemistry and is provided for educational purposes only. Mood does not provide consumption advice.
The 0.877 conversion factor assumes perfect conditions where every THCA molecule transforms into THC.
Real consumption methods achieve 70-80% activation at best, and then additional losses occur before the THC reaches your bloodstream.
Smoking delivers only 20-30% of calculated THC to your bloodstream.
Combustion destroys some cannabinoids, sidestream smoke carries away more, and your lungs don't absorb every molecule from the inhaled smoke. That 100mg calculated from your half-gram joint becomes roughly 20-25mg of THC that actually affects you.
This explains the disconnect between label math and lived experience.
A gram of 20% total THC flower calculates to 200mg, but smoking it delivers approximately 40-60mg to your system. Vaping improves efficiency slightly, typically delivering 25-35% of the calculated total.
Setting realistic expectations prevents disappointment.
When you calculate 200mg from your flower, understand you'll feel effects equivalent to 40-60mg if smoking or 50-70mg if vaping. This isn't about weak products—it's about honest chemistry.
What Different Product Types Mean for Your Calculations
Flower and THCA concentrates require the THCA × 0.877 formula because you're working with raw plant material that activates during consumption. Every time you light flower or heat a concentrate, you're triggering that conversion process.
Do I Need to Convert THCA for Edibles?
Edibles list active THC in milligrams per serving because manufacturers handle the conversion during production. When you see "10mg THC gummy," that's already-active Δ9-THC.
No calculation needed—the number on the package is what you're consuming.
Vapes contain activated THC in their oil, but your consumption temperature still affects how much vaporizes. Lower temperatures preserve more cannabinoids but may not fully activate everything in the oil.
Higher temperatures activate more completely but can degrade some compounds.
How Lab Testing Methods Change What You See
HPLC keeps THCA and THC separate because it tests at room temperature, giving you the raw cannabinoid profile before heat exposure.
This method shows exactly what's in your flower as it sits on the shelf.
GC testing heats samples during analysis, which partially converts THCA to THC before measurement. Results from GC analysis may show higher Δ9-THC numbers than HPLC because the test itself triggered some conversion.
We use HPLC testing for clean, separated values.
This gives you accurate THCA and Δ9-THC numbers for reliable calculations. When you apply the 0.877 formula to our HPLC-tested flower, you're calculating from true raw plant chemistry.
The Legal Context Behind THCA and Total THC
The distinction between THCA and Δ9-THC creates the legal framework that makes hemp-derived cannabis products possible. Compliance testing measures Δ9-THC in raw product—the molecule present before heating.
Mood offers millions of users hemp-derived THC, which is 100% legal and fully compliant cannabis. You may have heard that the legality of hemp-derived THC is currently under attack, which could threaten access for so many.
Read here to learn how to join the fight, and help us keep hemp cannabis accessible to all for a long time to come.
State regulations vary in how they handle THCA products. Some states apply total potential THC formulas to hemp compliance, while others follow the Δ9-THC standard.
Check your state's specific rules before purchasing.
THCA products trigger standard drug tests exactly like traditional cannabis.
Tests detect THC metabolites without distinguishing between hemp-derived and marijuana-derived sources. Your legal receipt doesn't provide drug test immunity.
Storage conditions affect your product's legal status over time. THCA slowly converts to Δ9-THC at room temperature, accelerating with heat and light exposure.
A product testing at 0.25% Δ9-THC when fresh might measure above 0.3% after months in poor storage, technically becoming non-compliant.
Important Disclaimer: Mood is not a medical or wellness authority. This article provides educational information about cannabis chemistry and calculations. Consult licensed medical professionals for health-related questions or concerns. Never use cannabis products if you're subject to drug testing, pregnant, or breastfeeding. Cannabis products are intended for adults 21 and older only.
You Can Now Calculate Total Potency from Any Label
You've learned to read COAs, apply the 0.877 formula, convert percentages to milligrams, and set realistic expectations about real-world delivery.
These skills work for any cannabis product with published lab results.
We provide the third-party lab data you need for informed choices. Every product comes with accessible COAs showing exact THCA and Δ9-THC percentages.
Transparency isn't marketing—it's how you make confident purchasing decisions.
The calculated number isn't what you'll feel, but now you understand why. Factor in 70-80% activation and 20-30% bioavailability for smoking, and your estimates match reality. Start with the math, then adjust for method.
