How this instrument works
Millilitres are cubic centimetres, exactly, and have been only since 1964. Before then, one litre meant whatever volume one kilogram of pure water occupied at maximum density, which careful measurement placed at 1.000028 dm³ — so older millilitre readings sit 28 parts per million above cubic centimetres. That year's General Conference on Weights and Measures cut water out of it and redefined the litre as one cubic decimetre flat. Litres and millilitres are not SI units proper, though SI accepts them for use alongside its own.
The US cup has stranger ancestry. It is one sixteenth of the US liquid gallon, and that gallon stays frozen at 231 cubic inches — Queen Anne's wine gallon of 1707, which America kept after Britain scrapped it for an imperial gallon of 4.54609 litres in 1824. Since 1959 an inch has been 25.4 mm exactly, so 2.54³ gives 16.387064 cm³, 231 of those make 3785.411784 ml with nothing rounded away, and one sixteenth of that comes to 236.5882365 ml. Put another way, your cup measure holds 14.4375 cubic inches.
Which is why 0.00422675283773 looks so unlovely: it is 1 ÷ 236.5882365, or 2000000⁄473176473 in fraction form, and 3 divides that denominator, so its decimal never settles down. Millilitres label every bottle, syringe and European or Australian recipe; cups rule American kitchens and almost nowhere else. Three rival cups are also in circulation. US nutrition panels use the legal cup of 240 millilitres set by regulation, while Australia and New Zealand measure with 250 millilitre metric cups. This page converts to that 236.5882365 ml customary cup which American cookbooks mean.
- Type your volume into Millilitres (ml) — 500 is preloaded as your starting point.
- Read US cups (cup) directly beneath. It recalculates on every keystroke; no button to press.
- Working from cups instead? Multiply your cup figure by 236.5882365 and enter that in Millilitres (ml).
- For kitchen work, round to two decimals and match your measuring set: 0.25 cup is one quarter measure, 0.0625 cup one tablespoon.
- Check which cup your recipe means before trusting any number — this pair uses only US customary cups.
Worked example — 500 ml of chicken stock
An American cook opens her Belgian soup recipe, which calls for 500 ml of chicken stock. Enter 500 in Millilitres (ml) and US cups (cup) returns 2.11337641887 — two cups plus something just under an eighth. That leftover eighth is 26.82 ml, or 1.81 US tablespoons, and the whole half-litre amounts to 16.907 US fluid ounces.
In practice you would pour two full measures and add two tablespoons, landing on 2.125 cups or 502.75 ml. Being 0.55% heavy vanishes into soup and would not trouble stew, though custard deserves better. Had you assumed the 240 ml nutrition-label cup instead, that same volume reads 2.0833, and measuring it out with real cups leaves your pot about 7 ml short.
Questions
Is 236.5882365 ml exact, or rounded off?
Exact, and provably so. The US liquid gallon is defined as 231 cubic inches; an inch is defined as 25.4 mm; 2.54³ is 16.387064 cm³, so that gallon comes to 3785.411784 ml with no approximation anywhere in sight. Divide by 16 and one cup is 236.5882365 ml. Every digit terminates because 231 and 2.54 are both definitions rather than measurements — nobody ever weighed water to get here.
Why does the multiplier 0.00422675283773 stop where it does?
Because it has to stop somewhere. Going from millilitres to cups means dividing by 236.5882365, and that reciprocal is exactly 2000000⁄473176473 — rational, with 3 among its denominator's factors, so its decimal expansion repeats without end. Twelve significant figures sits far past any physical relevance: across your 500 ml pour, truncating there shifts the answer by less than one trillionth of one cup.
Is the US cup the same as imperial or metric cups?
No, and those gaps are wide enough to wreck your bake. The US customary cup is 236.5882365 ml. Australia, New Zealand and Canada standardised on 250 ml metric cups, about 5.7% larger. Britain's old imperial cup ran to 10 imperial fluid ounces, roughly 284.13 ml, some 20% above US volume — though modern British recipes weigh ingredients instead. Japan's gō is 180 millilitres. Where the recipe stays silent, its country of origin usually answers for it.
Why does my nutrition label say one cup is 240 ml?
Because US food labelling runs on its own legal cup, rounded to 240 ml by regulation so serving sizes print cleanly. That sits 3.41 millilitres above customary volume, or 1.4% high. Nutrition panels, dietary guidance and hospital fluid charts all work in 240; recipes and measuring sets work in 236.5882365. Results here give you the second one.
Can I use this for flour, sugar or other dry ingredients?
Only where your figure is genuinely volume. Cups measure space, not mass, so 500 ml of sifted flour really is 2.11 cups of sifted flour. But recipes asking for 500 grams cannot be rescued by any volume factor, because one cup of flour weighs anything from 120 to 150 grams depending on how tightly it was packed. For mass, apply the density figure specific to that ingredient — or do what bakers do and weigh it.
Do dry and liquid measuring cups hold different amounts?
No — 236.5882365 ml in both. They differ in shape, not capacity. Liquid cups are clear jugs with headroom and pouring spouts, so you fill to the printed line without spilling; dry cups get filled past their brim and levelled off with straight edges. Tipping flour into such jugs usually overfills them, since there is no rim to level against, and that is where cup-based baking errors mostly begin.