How to Calculate Total THC from THCA on Labels

By Lorien Strydom
February 16th, 2026

Cannabis labels can feel like deciphering a secret code, leaving you wondering what "29% Total THC" actually means for your experience.

With terms like THCa, Delta-9, and THC percentages alongside milligrams per gram, understanding true potency and federal compliance can be confusing.

This guide breaks down the essential math and science, starting with the definitive formula for calculating Total THC potential, and teaching you how to convert those percentages into real-world milligram amounts.

By the end, you'll be able to decode any label with confidence and know exactly how to verify a product's strength using a Certificate of Analysis (COA) or home testing methods.

Table of Contents

• The Total THC Formula: Your Quick Answer
• Total THC vs THC: Decoding the Two Numbers on Your Label
• A Real Label Walkthrough Using a 29% Pre-Roll
• Where THC Numbers Come From and How to Verify Them
• What Label Percentages Mean for Smoking and Vaping
• Testing THC Percentage at Home
• Calculating THC Amount for Homemade Edibles
• Why Your 30% Strain Tested at 19%
• Concentrates and Drug Tests: Two Common Questions
• Reading Any Cannabis Label with Confidence

The Total THC Formula: Your Quick Answer

Total THC equals THCa percentage multiplied by 0.877, plus any existing THC percentage. The 0.877 factor accounts for molecular weight lost when THCa converts to THC during heating.

Here's the formula: Total THC = (THCa% × 0.877) + THC%.

This number represents the theoretical maximum cannabinoid content after heating. A 1g pre-roll at 29% Total THC contains roughly 290mg potential THC. Your actual intake will be lower because smoking and vaping lose some cannabinoids to side-stream smoke and incomplete conversion.

To convert mg/g to percentage, divide by 10. For example, 250 mg/g equals 25% THC.

Total THC vs THC: Decoding the Two Numbers on Your Label

Cannabis labels show two different numbers, and understanding both matters. THC shows active cannabinoid content before heating. Total THC shows potential cannabinoid content after heating. THCa shows the acid form that converts when smoked or vaped.

Raw flower contains mostly THCa and very little THC. This is why you'll see labels listing 28% THCa alongside just 0.2% THC. The plant naturally produces the acid form.

When you apply heat through smoking or vaping, THCa transforms into the compound that creates the familiar cannabis experience. The Total THC number captures this potential by calculating what you'd have after heating.

Some labels list milligrams per gram instead of percentages. The conversion is straightforward: divide mg/g by 10 to get the percentage. A product showing 220 mg/g contains 22% THC.

Is 20% THCa the same as 20% THC? No, but they deliver comparable effects after heating. The 0.877 conversion factor means 20% THCa becomes roughly 17.5% THC after heat exposure, producing similar potency to a 20% THC product once smoked or vaped.

Hemp-Derived THCa: Why High Percentages Can Be Federally Compliant

You might see products listing 29% Total THC while claiming federal compliance. This seems contradictory until you understand the legal framework.

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 the wellness of 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.

The key distinction is measurement timing. Federal compliance measures Delta-9 THC content before heating, while Total THC represents potential after heating. A product can show 29% Total THC because that percentage includes THCa, while the actual Delta-9 THC remains under the threshold.

A Real Label Walkthrough Using a 29% Pre-Roll

Looking at an actual product makes the numbers concrete. Mood's Kush Mintz pre-roll displays 29.01% Total THC on its packaging, along with a detailed terpene profile listing compounds like bisabolol, myrcene, limonene, and caryophyllene.

That 29.01% figure represents mostly THCa that transforms when heated, with Delta-9 content staying under regulatory thresholds for federal compliance. For a 1g pre-roll, multiply 1000mg by 0.2901 to get 290.1mg of potential THC.

The label also shows terpene composition. These compounds influence aroma and experience beyond just percentage numbers. Myrcene contributes to body relaxation, while limonene affects mood elevation. Looking at both cannabinoid percentages and terpene profiles gives you the complete composition picture.

Pre-rolls arrive already ground, which means you're trusting the testing that occurred before packaging. This is where Certificate of Analysis documentation becomes important for verification.

Where THC Numbers Come From and How to Verify Them

Laboratory testing generates the numbers you see on labels. High-Performance Liquid Chromatography (HPLC) is the industry standard because it measures cannabinoids at room temperature without converting THCa to THC during analysis.

Gas chromatography was used historically, but the heat involved in that testing method can convert THCa during the analysis itself. This creates confusion about what the original flower actually contained. HPLC keeps the compounds separate and provides clearer measurement.

Certificate of Analysis documents show the detailed breakdown. You can scan a COA in 10 seconds by looking for THCa%, THC%, Total THC, batch identification, test date, and lab name. These documents translate laboratory results into the percentages printed on product packaging.

The unregulated hemp market has quality variation between testing facilities. Some labs have been found inflating potency numbers. Chain of custody matters, especially for pre-rolls where you cannot inspect the flower yourself before consumption.

Mood provides third-party testing documentation for verification. Products include accessible COAs that show cannabinoid levels and confirm purity standards.

What Label Percentages Mean for Smoking and Vaping

Total THC assumes perfect conversion under ideal conditions. Real-world smoking and vaping don't deliver the full labeled percentage.

Combustion loses cannabinoids to side-stream smoke. The smoke you're not actively inhaling contains compounds that never reach you. Vaping is more efficient but still doesn't capture everything. Incomplete conversion means some THCa remains unconverted even with heat exposure.

This explains why a 25% product sometimes feels more potent than a 28% one. Terpene profiles affect experience. Consumption method matters. Individual factors like tolerance play a role. The percentage is one data point, not the complete story.

For flower, 20% THC is considered high potency suitable for experienced users. Concentrates range from 40% to 90%+, making 20% moderate by comparison. Individual tolerance and consumption method also affect perceived strength.

Think of Total THC as an upper bound rather than a guarantee. It tells you the maximum potential, assuming everything converts perfectly and you capture all the smoke or vapor. Real intake sits below that ceiling.

Testing THC Percentage at Home

Can you test your THC levels at home? Yes, three methods work for home verification: TLC chromatography kits like Alpha-Cat provide accuracy within a narrow range, colorimetric kits offer cheaper rough estimates, and handheld devices connect to smartphone apps for instant readouts.

Thin-layer chromatography kits separate cannabinoids on coated glass plates. You compare colored spots to a reference template. Alpha-Cat kits cost around €135 for 20–25 tests and take about 45 minutes to complete. A 100mg flower sample provides enough material for testing.

Colorimetric kits use chemical reagents that change color based on cannabinoid levels. These are less precise than TLC but cost significantly less. They work well for rough estimates when exact percentages aren't critical.

Is there a THC tester for your phone? Yes, devices like Purpl PRO and tCheck connect via Bluetooth to iOS and Android phones, displaying potency results through companion apps. Purpl PRO tests raw flower directly. tCheck requires material that has been heated or infused into oil, not raw bud.

tCheck devices cost between $250 and $400. Purpl PRO sits in a similar price range. These represent significant investments, but they let you verify any product's potency rather than trusting labels.

Each method has tradeoffs. TLC kits provide good accuracy for multiple cannabinoids. Colorimetric tests are cheap but imprecise. Handheld devices are convenient but require the right sample preparation. Choose based on whether you need exact numbers or just general verification.

Calculating THC Amount for Homemade Edibles

The same math applies to edible preparation. Start with flower weight in milligrams. One gram equals 1000mg. Multiply by THC percentage or THCa percentage times 0.877 for unconverted material. Divide by your number of servings.

Example: 3.5g of 20% Total THC flower contains 3500mg × 0.20 = 700mg potential THC. If making 14 servings, each contains roughly 50mg. This is a strong amount for most people.

Heating flower before infusion amplifies THCa effects when exposed to heat. Most home cooks heat at around 240°F for 30–40 minutes. This brings cannabinoid content closer to the Total THC assumption on labels.

Extraction into butter or oil won't capture 100% of available cannabinoids. Expect 70–80% efficiency with careful technique. This means your 50mg calculated serving might contain 35–40mg in practice. Start with smaller portions when testing homemade edibles.

Standard starting amounts are 2.5mg or less for new users. Experienced users might start at 5–10mg. Wait at least 90 minutes before considering more, as edible effects take time to develop fully.

Why Your 30% Strain Tested at 19%

Seed banks list genetic potential, not guaranteed harvest results. The same seeds grown under different conditions produce different cannabinoid levels.

Lighting intensity affects cannabinoid production. Nutrient availability matters. Plant health throughout the growing cycle changes potency. Even the specific location on the plant where samples come from creates variation. Top colas test differently than lower buds and sugar leaves.

Representative sampling is crucial but often poor in practice. Testing a single top nug doesn't guarantee the whole batch matches. Cannabinoids distribute unevenly throughout the plant.

This explains harvest disappointment when results come back below seed bank claims. You didn't do anything wrong. Genetic potential under perfect conditions differs from real-world growing outcomes. Your 19% result is still good flower, just not the theoretical maximum the seeds could produce.

Concentrates and Drug Tests: Two Common Questions

Concentrates span 40% to 90%+ THC, requiring different testing protocols. FTIR spectroscopy is common for quality control at these levels. Small measurement errors matter more when percentages are this high. A 2% variation at 75% potency represents significant amount differences.

Most home testing kits aren't calibrated for concentrate ranges. They work for flower percentages but become unreliable above 40%. Professional laboratory testing is more important for concentrates than for flower.

Is there a test to see how much THC is in your system? Drug tests measure THC metabolites at nanograms per milliliter cutoff levels in urine, not product potency. They answer whether you consumed THC recently, not how strong the product was.

Drug tests detect metabolites, not potency. Urine tests look for THC-COOH at specific thresholds. These tests can't tell whether you used a 15% or 30% product. They only detect that THC entered your system within the detection window.

Hemp-derived THCa products will cause failed drug tests despite federal compliance. Heat exposure creates the same metabolites regardless of the product's legal status. The testing can't distinguish between sources.

Reading Any Cannabis Label with Confidence

You can now parse THC vs Total THC instantly. You understand that Total THC represents potential after heating, not guaranteed intake.

You can convert mg/g to percentages in your head by dividing by 10. You know how to turn label percentages into usable milligram amounts.

Two paths exist for using this knowledge. You can verify numbers yourself using Certificate of Analysis literacy or home testing equipment. Or you can choose pre-tested products with accessible documentation that provide transparency without requiring verification work.

For readers who want convenience, products like Mood's Kush Mintz with accessible COAs and clear terpene profiles eliminate the verification burden.

The testing documentation this article taught you to read is already available, and the label provides the composition information you need to make informed decisions.

The formula stays the same regardless of product: Total THC = (THCa% × 0.877) + THC%. The label becomes a tool you understand rather than a mystery requiring guesswork.

You know what the numbers mean for actual consumption, and you can set realistic expectations based on your chosen method.