You pick up a jar at the counter, see "34% THCa" in big type, and assume that is the strength. Then a budtender points to a smaller line that reads "Total THC: 30.3%" and you wonder which one is real. Total THC is the number to trust. It is the math that estimates how much actual THC the flower can deliver once you heat it. That is the figure to use when you compare two products.
Here is the short version. Raw cannabis flower barely contains any active THC. It mostly carries THCa, an acidic precursor. Heat from a lighter, a vape coil, or an oven knocks a piece off that molecule and turns THCa into THC. Because the molecule loses a little weight in that conversion, you cannot just add the two numbers together. You multiply THCa by 0.877 first, then add the small amount of THC already present. Effects may vary. Please consume responsibly.
Why 0.877 and not 1.0
THCa is THC with an extra carboxyl group attached, a cluster of carbon and oxygen atoms. When you apply heat, that group breaks off and leaves as carbon dioxide. The process is called decarboxylation. The THC that remains weighs about 87.7% of the THCa you started with. So one gram of THCa cannot become a full gram of THC. It becomes roughly 0.877 grams. The 0.877 factor is just that mass ratio, locked in by chemistry, not a brand choice.
Why is the THCa percentage higher than the Total THC percentage?
Because THCa is heavier than the THC it becomes. When flower is heated, THCa sheds a carboxyl group as carbon dioxide and loses about 12% of its mass. So a 34% THCa flower converts to roughly 30% Total THC, never more. The bigger raw number is not the active strength.
Reading it on a New York label
New York's Office of Cannabis Management requires Total THC on every adult-use product, and the way it appears depends on the format. Inhalable products like flower, pre-rolls, and vape carts show potency as a percentage of weight. Edibles, drinks, and tinctures show it in milligrams, both per serving and per package, because you are dosing by the piece rather than by the gram.
- Flower and vapes: look for the Total THC percentage, not just the THCa line
- Edibles and drinks: read milligrams per serving first, then per package
- NY caps edibles at 10 mg of Total THC per serving
- Both Total THC and Total CBD are required on the label
Should I compare flower by THCa percentage or Total THC?
Use Total THC. THCa percentages can look dramatic but they overstate what you will actually consume, since the molecule loses weight when heated. Total THC reflects the THC potentially available after you light or vape it, so it is the fairer apples-to-apples number across two jars.
The big THCa number sells the jar. The Total THC number tells you what you are actually getting.
A worked example
Say a jar lists 32% THCa and 0.8% THC. Multiply 32 by 0.877 and you get about 28.1. Add the 0.8% of THC already present and Total THC lands near 28.9%. Notice it is lower than the 32% on the front, and that is normal. If a second jar shows 28% THCa with 1% THC, its Total THC is roughly 25.6%. The first one is stronger on paper, but the gap is smaller than the headline THCa numbers suggest.
You do not need to run the math at the counter. Every product on our menu lists Total THC, and our budtenders read these labels all day. Come into 45 Main Street in Hastings-on-Hudson, browse the menu at /order, and ask us to walk you through any cultivar. We will help you compare the numbers that actually matter and find something that fits how you want your day to go.