If you’re like us, you’re more interested in drinking than doing math. However, for home mixologists who want to geek out, here’s a little simple cocktail math that can help you determine how strong those homemade cocktails actually are. You may have measured how many ounces of liquor and other ingredients you put in your drink, but that doesn’t actually tell you the alcohol content. Here’s a quick way to figure it out.

You’ll need the following information:

- Exact measurements of each ingredient.
- The alcohol content by volume of these ingredients. (The “proof” of a spirit is equal to twice its alcohol content. So, for example, 80 proof means 40% alcohol by volume.)
- The total volume of your drink, including dilution from ice.

For example, let’s say you made a Cosmopolitan with the following recipe:

- 1.5 ounces of 80 proof vodka (40% alcohol)
- .5 ounces of 70 proof triple sec (35% alcohol)
- .5 ounces of cranberry juice
- .5 ounces of lime juice

It’s hard to tell exactly how much water is added by shaking this drink in ice but assuming you give it a good shake with a healthy amount of ice, it’s fair to guess that you’re adding about 25 percent (in this case .75 ounces).

The general formula is to take the volume of your liquor ingredients, multiply it by the percentage of alcohol by volume and divide that by the total volume of ingredients. Then multiply the whole thing by 100. So it’s (volume of liquor x alcohol by volume/total cocktail volume) x 100

For our Cosmo, it would look like this:

[(1.5 x .4) + (.5 x .35)]/3.75 ( the multiply the result by 100)

So we’d get 20.67% alcohol by volume for that homemade Cosmo. That makes it around 42 proof.

This is still an estimate, since the amount of water added by ice can vary widely. But if you get that part down to a science, you could get very close.