How this calculator works
For water, one millilitre weighs one gram at ordinary kitchen temperatures, so the numbers can be used almost interchangeably. Every other ingredient has a different density. Whole milk is about 1.03 g/mL, vegetable oil about 0.92 g/mL, all-purpose flour about 0.53 g/mL and granulated sugar about 0.85 g/mL. The calculator converts the USDA cup weight of the chosen ingredient into grams per millilitre, then applies it to the amount you enter.
Formula
grams = millilitres x density in grams per millilitre. millilitres = grams / density. Density is the USDA grams per cup divided by 236.588, the millilitres in one US customary cup.
Worked example
250 mL of whole milk weighs 250 x 1.031 = 258 g, because one cup of 236.588 mL weighs 244 g and 244 / 236.588 = 1.031 g/mL. The same 250 mL of vegetable oil weighs 250 x 0.921 = 230 g, and 250 mL of all-purpose flour weighs about 132 g.
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Frequently asked questions
Are millilitres and grams the same for water?
Almost. Water is about 0.998 g/mL at 20 degrees Celsius and 1 g/mL at 4 degrees Celsius. For cooking, treating 1 mL of water or a thin stock as 1 g introduces an error of less than half a per cent.
Why does a cup of flour weigh so much less than a cup of water?
Flour is mostly air between the particles. A cup of all-purpose flour weighs about 125 g, so it fills more than twice the volume of the same mass of water. Packing the flour into the cup reduces that air and increases the weight.
How do I measure millilitres without a jug?
One US cup is 236.588 mL, one tablespoon is 14.787 mL and one teaspoon is 4.929 mL. A Canadian 250 mL measuring cup is the metric cup and is a common substitute for a US cup in recipes written in Canada.
Does temperature change the conversion?
It changes density slightly, mostly for liquids. Water expands by about 0.4 per cent between 20 and 40 degrees Celsius. The cooking-scale effect is small, but the density of a hot syrup can differ enough to matter in candy making.