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. When scaling a recipe it’s important to know how to convert back and forth between different measurements.
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.
Keep in mind; some ingredients will have a ‘weight’ or percentage of importance in scaling, and so will need to be adjusted differently.
In the United States, liquid measurement is not only used for liquids such as water and milk, it is also used when measuring other ingredients such as flour, sugar, shortening, butter, and spices.
Dry measurements are not typically used in US recipes; dry measurements are used mainly for measuring fresh produce (e.g. berries are sold by the quart, apples by the bushel, or peck). Do not confuse dry measure with liquid measure, because they are not the same.