Kitchen Math and Recipe Conversions

Me and math don’t get along too good. So, in my junior year of college, we came to an agreement of sorts; I will try to use math as little as possible in my life, and math will try not to totally ruin that life. In my alter ego as a programmer, it makes things a little interesting from time to time, but in the kitchen, I’ll admit it’s pretty indispensable. Luckily, I only have to rely on a couple of math tricks to get the amounts I need when working with recipes that I need to scale when I use a different amount of the main ingredient each time I prepare that dish.

I love this scene from the movie Peggy Sue Got Married, mostly because I can relate to it wholeheartedly.

The good news is that kitchen math is mostly ratios, with only a couple of real formulas thrown in. Temperature conversion, for example.

Most of the recipes on my site are done by weight, so you can scale the recipes as needed. Or rather, I can scale the recipes as needed. But, most recipes you find in cookbooks are written for home kitchens, which means that they’re written in volume amounts. Here’s the problem. We all know that a pound of feathers weighs as much as a pound of lead. However, a cup of feathers weighs far less than a cup of lead. So we need to know how much each cup weighs, so we can know the ratio, also known as the density.

You with me so far?

There are sites online that will convert volume to weights, created by people way nerdier than I am. When I develop a recipe, I use volume measurements, since it’s easier to add another tablespoon or cup of an ingredient, rather than measuring on a scale as something is slowly burning on the stove. Then, when I have the recipe worked out and I’m happy with the flavors, etc. I convert the recipe from volume to weight. I do it all for you, dear readers.

The First Trick

There is one super wonderful math shortcut for figuring out the missing measurement when scaling:

a/b = c/d

or

a=(b*c)/d

Let’s say I have a recipe that calls for 2 kilograms of meat and 650 grams of potatoes. I want to make the recipe with 4.36 kilograms of meat, because that’s what I have. How much potatoes do I need? Multiply 4.36 * 650, and divide by 2. I’ll need 1.4 kilos of potatoes. Which makes sense. For a little more than double the meat, I’ll need a little more than double the potatoes.

The Second Trick

The other method I use frequently is to create a number that I can then multiply all of the other ingredients by to get to how much I’ll need for the scaled up recipe. So how does this apply in the kitchen? Let’s say I have a recipe that calls for 2.5 kilograms of meat. But, I have 4.25 kilograms of meat, because that’s what came in the package. I divide 4.25/2.5, which tells me that I have a multiplier of 1.7, or that I’m using 170% of the meat originally called for in the recipe. So if I need 330 grams of tomato sauce in the original recipe, I’ll need 561 grams in the scaled up recipe. If I need 30 grams of salt, I’ll now need 51 grams.

The great part of all this is that I create spreadsheets with these ratios, so I only have to look up the weight to volume measurements once, and then I can use the same recipe over and over again.

This is especially important when I’m working with cured meats, or making the pink salt itself.

Note to editors: That first sentence is probably still making you cringe. I employed artistic license to juxtapose the scholarship of an article about weights and measurements with a sentence that is clearly meant to be nearly illiterate. With malice aforethought.