US customary and metric cups
This site defines its US customary cup as 236.5882365 ml. Its metric cup is 250 ml. A result expressed in cups therefore needs a system label, even when the ingredient and amount stay the same.
For example, the number of metric cups required to hold a fixed volume is smaller than the number of US cups, because each metric cup is larger. This is a difference in measuring units, not a change to the ingredient.
Why 240 ml also appears
Practical kitchen references often round unit values for convenience. NIST’s kitchen table presents a 240 ml cup equivalent alongside rounded spoon and fluid-ounce values. That is useful kitchen guidance, but it is different from an exact US customary calculation.
This converter keeps those distinctions visible. It does not silently treat 236.5882365, 240 and 250 ml as the same quantity. If your recipe explicitly defines a 240 ml cup, follow that recipe definition.
Spoons need a system too
The metric and Australian settings both use a 250 ml cup, but their tablespoon values differ in this calculator: 15 ml for metric and 20 ml for Australian. A teaspoon is 5 ml in both settings.
Historical Imperial volumes differ from US customary measures. The main converter offers US customary, metric and Australian settings. A modern British recipe may use metric quantities, so do not assume it requires a historical Imperial cup.
Keep one convention throughout
Look for measurement notes near the ingredient list, in the recipe introduction or on the author’s help page. If the recipe supplies grams, those weights may remove the need to identify its cup convention for dry ingredients.
Once you choose a system, use it for every volume amount in that recipe. When switching systems in the converter, read the new number rather than keeping the old cup count. Keep both the numeric result and its label in any copied or printed measurement.