From About.com's Culinary Arts page
Let's say you have a recipe that serves 6 people, but you want to make it for 2 people instead. Or even trickier, what if a recipe serves 4 people, but you need to make it for 6? Or 14?
It doesn't matter whether you're increasing a recipe or decreasing it — the procedure for adjusting the ingredient quantities for a different number of portions is the same. We call this scaling a recipe.
The first thing you need to do is calculate your conversion factor, which is a number you're going to use to convert all the quantities. There's a tiny bit of math involved, but it's OK to use a calculator — that's what they're there for!
To find your conversion factor, simply divide the desired number of servings by the original number of servings. The resulting number is your conversion factor. Here's the formula:
———————— = conversion factor
Scaling that 10-portion recipe down to six portions involves two steps:
Let's work through a simple example to illustrate how this works. Say your recipe calls for 2 quarts of chicken stock. All you need to do is multiply 2 quarts by your conversion factor of 0.6:
2 quarts × 0.6 = 1.2 quarts chicken stock
Great! But wait a second... What exactly is 1.2 quarts? Well, questions like that are why most of the world uses the metric system. The rest of us are going to have to convert 1.2 quarts into ounces. If we consult this handy cooking conversion tool, we see that there are 32 ounces in a quart, so:
32 × 1.2 = 38.4 ounces
We can round that down to about 38 ounces, but that's still kind of a weird amount. It'd be more clear if it were given in cups, wouldn't it? Our cooking conversion tool reminds us that there are 8 ounces in a cup, so:
38 ÷ 8 = 4.75
Which means 1.2 quarts is equal to approximately 4¾ cups. That's all there is to it!
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