Calculator
Recipe scaler and kitchen unit converter
This is for anyone cooking for more or fewer people than a recipe was written for, or following a recipe that uses different units than your measuring tools. Paste the ingredients, say how many servings the recipe makes and how many you want, and every line that starts with an amount is multiplied for you. The converter below handles spoons, cups, weight and oven temperature.
Scale a recipe
Worked example (shown when scripts are off): scaling a 4-serving recipe to 6 servings multiplies every amount by 1.5, so 1 1/2 cups of rice becomes 2 1/4 cups and 2 tablespoons of oil becomes 3 tablespoons.
Convert a measurement
Worked example (shown when scripts are off): 1 US cup is about 237 millilitres, and 350 degrees Fahrenheit is about 177 degrees Celsius.
Before you rely on it
Volume and weight are different things. One cup of flour and one cup of honey weigh very different amounts, so this tool never converts cups to grams. Use a kitchen scale and the weights printed in the recipe when it gives them.
How the math works
Scaling uses one multiplier: the servings you want divided by the servings the recipe makes. Four servings to six is 6 divided by 4, or 1.5, and every amount is multiplied by it. The results are rounded to the nearest common kitchen fraction (eighths, thirds and sixths), because 2.27 cups is not something you can measure. Lines that begin with a range such as 2-3, or with no amount at all, such as salt to taste, are left alone so you can decide by hand.
The converter uses fixed US measures: 1 teaspoon is 4.93 millilitres, 1 tablespoon is 14.79, 1 fluid ounce is 29.57, 1 cup is 236.59, 1 pint is 473.18 and 1 quart is 946.35. For weight, 1 ounce is 28.35 grams and 1 pound is 453.59 grams. Temperature uses Celsius equals (Fahrenheit minus 32) times 5/9. Cups and spoons from other countries differ slightly, so a metric recipe is easier to trust if you have a scale.
Limits when you scale
Straight multiplication works well for most savory dishes cooked in a pot, but it gets less reliable at the extremes. Doubling is usually safe. Tripling or halving a lot is where problems start. Salt, strong spices and leavening such as baking powder often need a lighter hand than the math suggests, so add part of the scaled amount and taste. Cooking time does not scale with the amount of food: a bigger batch in a bigger pan may take longer to heat through, while a half batch in the same pan can cook faster or scorch. Baked goods are the most sensitive, because pan size changes depth and the way heat reaches the middle. If the pan changes, treat the first attempt as a trial.
Eggs are the classic trouble spot. If scaling gives you 1 1/2 eggs, beat one egg and use about half of it by volume. For anything with meat, poultry or eggs, scaling the recipe does not change the safe internal temperature, so check it with a thermometer using the safe temperature and storage guide.
Where this comes from
The unit values follow from the legal definitions of the US customary units: the US gallon is exactly 231 cubic inches (3.785 litres), which gives the cup, spoon and ounce volumes above, and the avoirdupois pound is exactly 0.45359237 kilograms. The temperature formula is the standard one. We did not measure any of this ourselves; the checks were done by running the formulas against known values. The rounding to kitchen fractions and the note that salt and leavening may need adjusting are general cooking practice, not tested here. This is general information for home cooks, not professional advice.