Cups to Milliliters Converter

The US cup was never designed around the metric system — it's defined as 8 US fluid ounces, and a US fluid ounce is fixed at exactly 29.5735295625 mL (derived from the old US gallon of 231 cubic inches). Multiply that ounce by 8 and you get 236.588 mL, rounded to six significant figures. Because the definition traces back to cubic inches rather than liters, the result is a repeating, non-round decimal — the same reason 1 inch converts to 2.54 cm instead of something tidier.

No. Australia, New Zealand, and the UK largely cook with a 250 mL 'metric cup,' which is about 5.6% larger than the US cup's 236.588 mL. Recipes that say simply 'cup' without specifying US or metric can be off by roughly 13-14 mL per cup — small in a single cup, but it adds up fast when a recipe calls for 4 or 5 cups. This converter uses the US customary cup (236.588 mL), the standard in American recipes and nutrition labels.

Because the underlying conversion factor, 236.588 mL per cup, is itself precise to six significant figures, and scaling it (for 2, 3, or 5 cups) can introduce further fractional mL. Showing the full decimal — e.g., 0.33 cup = 78.074040 mL — avoids compounding rounding errors if you're scaling a recipe up or measuring in a lab. For everyday cooking, rounding to the nearest mL or half-teaspoon is fine.

It's a common assumption because 500 mL 'feels' like 2 cups, but 2 US cups actually equal 473.176 mL — about 27 mL (roughly 1.8 tablespoons) short of half a liter. The gap comes from the cup being built on the US customary system (via fluid ounces and cubic inches), not the metric system, so round numbers in one system rarely land on round numbers in the other.

The most common mistake is rounding the conversion factor itself — using 240 mL per cup (a number popularized by some nutrition labels and casual metric guides) instead of the precise 236.588 mL. For a single cup, that's only a 3.4 mL difference, negligible in most recipes. But if you're scaling a recipe up — say, batch-cooking 20 cups of a syrup or brine — that same rounding error multiplies to nearly 70 mL, enough to throw off a delicate ratio like a cocktail syrup or a chemical solution. The safest approach is to use the exact 236.588 mL/cup factor for anything scaled by more than 4-5x, and only reach for the rounded 240 mL shortcut when eyeballing a single-cup measurement in a home kitchen.

The imperial cup, once used in the UK and Commonwealth countries, was defined as half an imperial pint and equals about 284.131 mL — roughly 20% larger than the US cup's 236.588 mL. It's been almost entirely retired since the UK went metric in the 1970s-80s, replaced by the 250 mL 'metric cup' in modern British and Australian recipes. So if you're converting an older British cookbook, neither this converter's 236.588 mL factor nor the 250 mL metric cup applies — you'd need the 284.131 mL imperial figure instead. Always check a recipe's country of origin and publication era before assuming which 'cup' it means; the three definitions differ enough to noticeably change a dish.

Multiply 2.5 by 236.588 to get 591.47 mL — but note that's a volume measurement, and flour's actual weight per cup varies with how it's scooped (roughly 120-150 g per cup depending on technique). If your recipe is measuring a liquid, like milk or oil, 591.47 mL is a direct, reliable substitute for 2.5 cups. For dry ingredients like flour, sugar, or cocoa, volume-to-volume conversion (cups to mL) is fine if you're just swapping measuring tools, but weighing in grams is more accurate — which is exactly why most professional bakers and European recipes skip volume for dry goods entirely and use a scale.

The cup as a standardized US recipe unit dates to Fannie Farmer's 1896 Boston Cooking-School Cook Book, which popularized precise, standardized measuring cups and spoons over the vague 'a piece of butter the size of an egg' instructions common before it. The US cup was then formalized as 8 US fluid ounces, itself derived from the US gallon of 231 cubic inches set by law in 1836. The milliliter, by contrast, is far older in concept — it's part of the metric system devised during the French Revolution in the 1790s, defined via the liter, which was originally set as the volume occupied by one kilogram of water at its temperature of maximum density.

Use milliliters. Cups are too coarse a unit for medicine dosing — a household cup measure can easily be off by several milliliters depending on how you fill it, and pediatric and liquid medications are dosed in mL (or fractions of a mL) precisely because small errors matter for safety. Pharmacists and pediatricians provide oral syringes marked in mL for exactly this reason, not cup markings. This converter is built for recipe and cooking-scale conversions, not medical dosing — if you're measuring medicine, always use the mL markings on the syringe or cup provided with the product rather than converting from a cup measurement.