THCa to THC Conversion Calculator
Use this calculator to determine the theoretical Total THC percentage of cannabis products after decarboxylation. This tool calculates the conversion of THCa into Delta-9 THC, accounting for the loss of molecular weight that occurs during heating.
Understanding the THCa Conversion Formula
When looking at laboratory tests for cannabis flower or concentrates, you will often see high levels of THCa (Tetrahydrocannabinolic acid) and low levels of Delta-9 THC. This is because the plant primarily synthesizes the acid form (THCa), which is non-intoxicating.
To convert THCa into the active psychoactive compound Delta-9 THC, heat must be applied. This process is called decarboxylation. During this chemical reaction, the carboxyl group (-COOH) is removed in the form of carbon dioxide (CO2) and water vapor. Because you are losing a piece of the molecule structure, the final weight of the THC is less than the original weight of the THCa.
The Math: The 0.877 Constant
The molecular mass of THCa is approximately 358.48 g/mol, while the molecular mass of THC is approximately 314.47 g/mol. When you divide the mass of THC by the mass of THCa (314.47 / 358.48), you get approximately 0.877.
This means that for every 1 gram of THCa, you only yield 0.877 grams of THC after perfect decarboxylation. The standard industry formula used by labs and regulators is:
Why Use This Calculator?
Consumers often simply add THCa and THC numbers together (e.g., 20% THCa + 1% THC = 21%), but this is inaccurate. Due to the molecular weight loss described above, the actual "Total Potential THC" is always lower than the raw sum.
Example Calculation
If you have a strain testing at 25% THCa and 0.5% Delta-9 THC:
- Step 1: Convert THCa: 25 × 0.877 = 21.925%
- Step 2: Add existing Delta-9: 21.925 + 0.5 = 22.425%
- Result: The Total THC is 22.43%, not 25.5%.
Calculating Milligrams (Edibles and Dosing)
This calculator also converts the percentage into milligrams, which is crucial for making edibles or understanding dosage. The conversion is straightforward:
1% THC = 10mg per gram of flower.
If your final Total THC is 20%, that means there are 200mg of active THC in every gram of flower. By entering the total weight of your flower in the calculator, you can estimate the total milligrams available for your infusion or tincture.