Cups to Milliliters

The two units

The US customary cup is defined as exactly 236.588 milliliters, or 8 US fluid ounces. The US fluid ounce itself is defined as exactly 1/128 of a US gallon, which is 1/231 of a cubic inch multiplied by 1,728 — a chain of definitions that resolves to 29.5735 mL per fluid ounce. So the US cup is 8 × 29.5735 ≈ 236.588 mL.

The milliliter is one thousandth of a liter, which itself is defined as one cubic decimeter. The liter and milliliter aren't strictly SI units (the official SI volume unit is the cubic meter), but they're so widely used in cooking, medicine, and chemistry that they're effectively universal.

Important: the US cup is not the only cup. The UK imperial cup is 284.131 mL (about 20% larger), although the UK rarely uses cups in recipes anymore. The metric cup, used in Australia and some other metric-country recipe books, is exactly 250 mL. Most recipes from a US source mean the US cup (236.588 mL).

The formula

milliliters = cups × 236.588

Round to 237 mL for everyday cooking; the 0.588 mL difference is irrelevant for any liquid measurement. Round to 240 mL only if you're using a metric "cup" definition.

When you'd use this conversion

Cooking is the dominant use case. American recipes use cups for liquids and many dry ingredients; metric recipes use milliliters (or grams for dry ingredients). Scaling a US recipe to metric — or following an American recipe with metric measuring equipment — requires this conversion.

Bartending is another routine context. International cocktail recipes often use milliliters (a "30 mL" pour is a US 1 oz pour). Mixology training in metric countries uses mL throughout; US bartending tends to use ounces.

Medical dosing for liquid medications uses milliliters universally — even in the US. Pediatric drug doses, IV bag volumes, and over-the-counter liquid medications all label in mL. A "1 teaspoon" dose of children's medication is 5 mL by international convention, which is actually slightly different from a US legal teaspoon (4.93 mL) but close enough that it doesn't matter for drug dosing.

Common mistakes

Using the wrong cup definition is the biggest pitfall. A US recipe scaled up using a metric cup measuring set (250 mL cups) will produce about 6% too much of everything — usually not catastrophic for cooking, but enough to throw off baking ratios. If you're following a US recipe, use US measuring cups, not metric.

Treating volume measurements as if they were weight measurements is the other big problem, especially for flour. A cup of flour can weigh anywhere from 100 g to 150 g depending on how it's measured (spooned vs scooped, sifted vs unsifted). For precise baking, weigh ingredients when possible. Volume-to-mL is fine for liquids; volume-to-grams needs ingredient-specific density.