There are plenty of calculators and formulas available online that purport to tell you the amount of THC in, say, each brownie in a pan. But these calculations can be totally off-base, as many have learned via hard-won experience.
Here's why it's so hard for home chefs to calibrate the dose.
1. Flawed formulas
Even if you've followed a recipe religiously, some formulas for calculating the THC per portion tend to result in dosage information that's impossibly high. The testers at Leafly thought they'd somehow made brownies that were 40 times the recommended dose of THC, until they realized their calculations didn't take into account the damage that's done to the THC, CBD, and various terpenes in the time required to extract them. It's also noteworthy that the conversion rate for THCA - the non-psychoactive acid in cannabis that gets broken down during the heating process to yield THC - is 0.88, not an equivalent amount of THC. All things you have to consider in your math.
2. Inefficient extractions
Depending on which edibles producer you ask, cannabutter only extracts between 30 and 60 percent of the cannabinoids and terpenoids in the cannabis used - with a wide range of potential potencies in between. Certain oils, like canola and vegetable oil, are even less effective than butter or coconut oil at extraction. You can cut down on the uncertainty by using concentrates to make cannabutter - provided you have a good idea of your concentrate's potency.
3. Poor portioning
Most people don't realize that "each cannabinoid has a different molecular weight, so they will settle in different places," as Lena Davidson of Botanica tells Leafly. That means cannabutter from the bottom of the container will have different effects than that skimmed from the top. Another way to get consistency with your baking is to either portion the butter vertically, or stir the product well - and never take shortcuts with measurements.
4. Tricky testing methods
In professional kitchens, producers first assess the cannabinoids and terpenes in the flower they're using, then test the extract again to determine how well the extraction worked, and finally test the plant matter that's left over to figure out the amount of cannabinoids and terpenoids left behind. Testing at multiple stages enables the pros to get a way more accurate read on the amount of THC in the edibles they're producing - a level of precision out of reach for most home cooks.
As in all things marijuana-related, when testing out a new recipe, start slow, and measure portions carefully (ideally with a ruler). And, as Leafly advises, "when in doubt, assume that the maximum amount of THC made it into your final product; you can always eat more if you find you were wrong."