One of the most common questions among medical cannabis users is how to determine the THC content of a homemade edible.

When I started writing about cooking with cannabis, I taught people how to estimate a reasonable THC dosage range to use in their cooking, just as cannabis cooks have been doing for thousands of years. Determining this “dosage window” involves balancing factors such as plant strength with the tolerance levels of the people consuming the food.

It’s difficult to get a precise measurement if your plant matter hasn’t been lab-tested. That involves multiple rounds of complex analysis. Even if you don’t know the exact percentage of certain cannabinoids, you can get a pretty close estimate, all it takes is a simple formula.

But instead of a reasonable dosage window with variations of 10 – 15 milligrams, wouldn’t it be great to know exactly how many milligrams of THC per serving your homemade edibles contain? There’s a formula you can use to get a pretty close approximation, even when the plant matter you are using has not been lab-tested. Is this formula totally foolproof? No, because THC levels can vary widely, but it will give you a pretty good idea.

However, if you are cooking with cannabis that HAS been lab-tested, you can use this formula to calculate even more precisely just how many milligrams of THC—and even CBD—per serving your homemade edibles contain.

I’m going to explain the formula here, but don’t worry about doing the math because there’s a handy Marijuana Dosage Calculator tool that does all the work for you.

Determine THC Percentage

For the sake of argument, let’s say that you do not know how much THC is in the plant material you are using, since most people won’t. A U.S. government study in 2009 said the national average of THC is 10 percent, but we know that not all weed is created equal.

Reportedly, the government grown cannabis from the University of Mississippi that is supplied to researchers tops out at a measly 3 percent THC, whereas a 2015 Colorado study that analyzed 600 samples from that state saw some top shelf strains containing a whopping 30 percent THC.

If you are cooking with schwag—low quality brick weed, trim or with government weed—use a THC content closer to 3 percent to start your estimate. If you know that your plant material is more potent than schwag, you might want to start your estimate with 10 percent or slightly higher.

But since Uncle Sam says average marijuana contains 10 percent THC, that’s what we will use in our example. It’s also a nice round number that makes it easier for people who are mathematically challenged to grasp the concept.

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The Formula





You don’t have to hire an accountant to work out how much THC is in your bud. But there are a couple of (mostly easy) calculations we need to make.

We measure THC by the milligrams (mg.) So first, we need to convert our flower weight (grams) to milligrams.

1g = 1000 milligrams

Then, we take the THC% and calculate its weight in milligrams.

Start your estimate with an average THC percentage.Low-quality cannabis or trim can contain as little as 3 percent THC, while top-shelf strains can average 25 percent or more. Government guidelines put the national average quality at 10 percent.

We’ll assume yours is 10 (if you don’t have the exact number from lab testing) to demonstrate the equation using a round number. First, you multiply your THCA by 1000 to get your mg/g of THCA

10% THCA x 1000 = 100mg of THCA per gram of cannabis

The conversion rate of THCA to THC is 0.877

100mg THCA x 0.877 = 87.7mg of THC per gram of cannabis

So, one gram of 10% cannabis contains 87.7 milligrams of THC as long as there was no THC in the cannabis to start with. If there was 0.2% THC in your cannabis before you decarboxylate then you must add that in as well.

0.2% THC x 10 = 2mg

2mg + 87.7mg = 89.7mg of THC per gram of cannabis

Next, you divide the amount of THC in your recipe by the number of servings it makes to get the per-serving dose. For example, suppose you make cannabutter with a cup of butter and a cup of average-quality ground cannabis (about 7 grams). Multiply 7 by 89.7 (7 x 89.7), and you have 627.9 milligrams of THC in the butter. If you used half the cup of butter to make 24 cookies, the batch would contain 313.95 milligrams of THC. Divide that by 24 (the number of servings), and you know each serving contains approximately 13 milligrams of THC.

Moving on, the amount of THC in a given recipe will depend on the amount of butter used.

To recap, first you need to estimate the percentage of THC in your plant material (or use the numbers from the lab test) and multiply that by 1000 to get the per milligram amount.

Next, calculate the number of milligrams in your infusion. Also take in to acount the amount of infusion you will use to make your recipe (if you will use 1/2 of the infusion divede by 2). Divide that by the number of servings your recipe makes, and you will know the per serving dose.

You can use this formula to create recipes that always ensure you are delivering a THC dose that meets your needs.

If you find a given recipe delivers too strong of a dose, cut the amount of cannabutter or oil and dilute with regular butter or oil to make up the difference. Cookies not strong enough? Add more THC to your recipe with some decarboxylated kief, hash or hash oil.

Beginners should start off with as little as 5-10mg THC per serving, and work their way up.



Tips On Making Your Own

Don’t throw in too much cannabis. Against popular belief that half an ounce of cannabis makes a cup of cannabutter, lipids in oils can only bind with so many cannabinoids. Anything extra is wasted. As in the example above, a 1:1 ratio of butter to cannabis will do.

Don’t forget to decarboxylate your cannabis before cooking with it – raw cannabis not only tastes bad, but renders your edibles ineffective.

Do stir your batter like your life depends on it. This will ensure the cannabutter is evenly distributed and the right dose makes it into each serving.

[Updated, originally published 2.3.2017]

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