I know I’ve been torturing you with these baking math posts. I know that it’s far less compelling than recipes, or lovely photos, or new insights about pastry. But, for those of you who really want to up your baking game, you’ll be amazed by how learning a little math makes baking so much easier.

Take, for instance, the problem of scaling up recipes. Let’s say you have a cookie recipe that yields 12 cookies. But you’re going to a party with 40 people, and you want to bring enough cookies for each guest.

Now, before I embraced baking math, I would look at that recipe and say, “well, I guess I’ll make a quadruple batch, which will make 48 cookies – and I’ll just have some left over.” But there’s no need to make extra cookies – instead, you can change your batch size to make exactly 40 cookies.

All you need is the recipe conversion factor, which lets you convert your recipe to different sizes. This sounds like a very fancy equation, but it’s actually quite common sense. You divide the number of cookies you want to make, by the number you have (the current yield), to get a “factor’ that you can multiply all your ingredients by to change the batch size. Written out in formula form, it looks like this:

Recipe Conversion Faction (RCF) = Want/Have

In this case, we’ll divide the batch size we want to make (40) by the batch size we have (12) to get our recipe conversion factor.

40 (yield we want) /12 (yield we have) = 3.33 (Recipe Conversion Factor)

Now we know that we have to multiply all our ingredients by 3.33 to get the batch size we want. For instance, if we were making these sugar cookies, we’d multiply all the ingredients by 3.33. I already converted the recipe to ounces and the smaller weights (teaspoons) to grams – let’s just pretend it yields 12 cookies for this example’s sake (note – because my scale only weights grams in whole units, I rounded all the gram conversions to the nearest whole number).

The math would look like this:

13.75 oz all-purpose flour x 3.33 = 45.79 oz all purpose flour

5 g baking soda x 3.33 = 17 g baking soda

3 g baking powder 3.33 = 10 g baking powder

8 oz butter, softened x 3.33 = 26.64 oz butter, softened

10.5 oz white sugar x 3.33 = 34.97 oz sugar

1.75 oz (1 piece) egg x 3.33 = 5.83 oz eggs

4 g vanilla extract x 3.33 = 13 g vanilla extract

So there you have it! Once you know the recipe conversion factor, you can always make the exact batch size you want. Yes, it may not seem like a big deal to make some extra cookies, but when you’re making a bunch of cookies frequently, it’s nice to know that you can make the exact batch size you want, every time.

And yes – can you imagine doing this type of conversion if you were using cups? If you multiplied 2 ¾ cups of flour by 3.33 you’d end up with 9.16 cups of flour. I mean, I’m sure there’s a way you could measure it using a volume measurement- but it would take way too long for me to figure it out. Really, that’s the hidden secret about this baking math stuff – it actually helps you do less work, and work more efficiently. It’s a win-win all around.

{ 8 comments… read them below or add one }

I appreciate this series so much. I know it won’t make NYT headlines and I know it takes a lot of work to put together, but your baKing Karma will prosper.

One day I hope to be a baking math ninja instead of having to use my fingers to count how many eggs are in a one-dozen carton.

Ah, thanks Becky! I know it’s way less sexy than cupcakes but I think that knowing stuff like this is the key to becoming a better baker. And there’s some stuff i want to share later this week (or next week) about ways you can use the RCF to do really cool stuff – like convert recipes between pan sizes, or scale a recipe up or down if you have less of an ingredient than you need. So cool – and so helpful.

I’m so glad you liked the series!

How do you do a portion of an egg? Do you round to the nearest egg, or scoop some of the white out? Or some of the yolk?

You use the weight of the egg to figure out what the portion of the egg would be. So, a whole egg (white and yolk) is 50 g. So, since we need .83 of an egg, I multiply 50 by .83 and get 42 g. The total weight of the eggs in the recipe should be (50g x 5) + 42g, or 292 g.

To weigh the 42 g portion of a whole egg, whisk it together so that the egg and yolk are somewhat combined, and then weigh out the extra 42 grams that you need. Or, to be even more accurate, you can whisk together 6 eggs and then measure out 292 g.

Damn! That’s precision, I like it! I had always wondered how to scale up recipes with eggs… Do you just use the extra smidgen for the next recipe?

Yes, you can save it an use it the next time, or you can use it for egg wash. Or throw it out. If it’s, like, 10 g of egg then I usually just toss it – especially if I’m not baking anything for awhile.

And see, this is what I’m talking about – baking math makes it possible to be so precise!

Maybe I am just a big nerd, but I’ve loved this series, especially the second post with the mass-volume conversions.

For this part of recipe conversion, I like to use a spreadsheet so that the values get automatically calculated for me with a click and drag. I’m lazy.