Recipe Scaler

How the scaler works

It finds one number, the scaling factor, and multiplies every amount by it.

factor = servings you need / servings the recipe makes

A recipe for 4 that needs to feed 10 has a factor of 10 / 4 = 2.5. A batch of 48 cookies cut down to 18 has a factor of 18 / 48 = 0.375. “Servings” can be anything you count: portions, cookies, muffins, loaves.

Multiplying is the easy part. The useful part is what comes after, because 0.375 of 3/4 cup is 0.28 cup and nobody owns a measure for that. The scaler rewrites each result in measures you have:

• It moves up a unit when the amount fits one. 6 teaspoons becomes 2 tablespoons, 16 tablespoons becomes 1 cup, 1,500 grams becomes 1.5 kilograms.
• It moves down when the amount is too small for the original unit. Half of 1/4 cup becomes 2 tablespoons.
• When nothing fits, it combines measures. Half of 3/4 cup is written as 1/4 cup plus 2 tablespoons.

Grams and milliliters are left as plain numbers, since a scale or jug can read any value.

Worked example

A chocolate chip cookie recipe makes 48 and you want 24. The factor is 24 / 48 = 0.5.

• 2 1/4 cups all-purpose flour becomes 1 cup plus 2 tablespoons
• 1 tsp baking soda becomes 1/2 teaspoon
• 1 cup butter becomes 1/2 cup
• 3/4 cup packed brown sugar becomes 1/4 cup plus 2 tablespoons
• 2 large eggs becomes 1
• 2 tsp vanilla extract becomes 1 teaspoon

Press “Try an example” above to run this recipe yourself.

When the factor is not a round number

Halving and doubling are the easy cases. A recipe for 6 that needs to serve 4 has a factor of 4 / 6 = 0.67, and the results are still measurable:

• 1 cup becomes 2/3 cup
• 1 tablespoon becomes 2 teaspoons
• 3 eggs becomes 2
• 450 grams becomes 300 grams

What it understands

Paste the ingredient list as it is written, one ingredient per line. The scaler reads:

• Fractions and mixed numbers: 3/4, 1 1/2, and the single characters ½ and ¼
• Decimals: 1.5, 0.25
• Ranges: “2-3 cloves garlic” becomes “4 to 6 cloves garlic” when doubled
• Units written long or short: cups, c, tablespoons, tbsp, T, teaspoons, tsp, t, ounces, oz, pounds, lb, grams, g, kg, ml, l
• Counted items with no unit: 3 eggs, 2 onions
• Lines with no amount, such as “salt to taste”, which pass through unchanged

Anything after a comma is kept as a note, so “1 cup butter, softened” stays softened.

What does not scale in a straight line

The scaler marks these lines with a short note.

Eggs. Scaling can leave you with half an egg. Beat one and measure out part of it, or round to a whole egg if the recipe is forgiving.

Salt, spices and other seasoning. A tripled stew does not always want triple the cayenne. Add a little less than the scaled amount, taste, and adjust at the end.

Yeast, baking powder and baking soda. These usually scale well for a half or double batch. For very large or very small batches, the scaled figure is a starting point.

Two things are not in the ingredient list at all:

Pan size. Twice the batter in the same pan is twice as deep. Use two pans, or a pan with twice the area.

Time and temperature. Keep the oven temperature the same. Cooking time follows the thickness of the food, so start checking at the original time and go from there.

Tips and common mistakes

Check the yield before you start. The most common error is entering the number of servings you want in both boxes, or reading “serves 4 to 6” as 4 when the writer meant 6.

Scale once, then write it down. Recalculating in your head halfway through is how a half batch ends up with a full measure of salt. Use Copy or Print and cook from the new list.

Be careful with very large factors. Home recipes are tested at their written size. At four times the amount and beyond, mixing times, pan crowding and evaporation all behave differently, so make a double batch twice if you can.