Cups to Ounces Converter (US cups and fluid ounces)

This cups to ounces converter turns US cups into US fluid ounces and fluid ounces back into cups. Type an amount, pick the direction, and it gives the converted volume along with the same amount in millilitres, tablespoons, the 240 mL cup printed on Nutrition Facts labels, and the weight that volume would have if it were water.

The relationship is fixed by definition. NIST Handbook 44 defines the US gallon as 231 cubic inches, the cup as one sixteenth of a gallon and the fluid ounce as one 128th, so a cup holds exactly 8 fluid ounces. Nothing is measured or rounded in that step. The only rounding on this page is in the millilitre, label cup and water weight figures, and each card says how many places it shows.

The ounce in this converter is the fluid ounce, a unit of volume. Many searches ask how many "ounces" are in a cup without saying which ounce, and for liquids that almost always means fluid ounces. If your recipe or package gives a weight in ounces instead, see the section on weight ounces below.

1. Type the amount. Fractions go in as decimals: a half cup is 0.5, three quarters is 0.75 and one and a half cups is 1.5.
2. Choose Cups to fluid ounces if your number is in cups, or Fluid ounces to cups if it is in fluid ounces.
3. Read the result at the top. The cards below repeat the volume in fluid ounces, cups, millilitres and tablespoons, then in 240 mL label cups, then as the weight of the same volume of water.

The preset buttons load one cup, three quarters of a cup and six fluid ounces. Two tables below the converter list common amounts in each direction, from a quarter cup to 16 cups and from 1 to 64 fluid ounces, and each downloads as a CSV file.

1. Choose the starting unit. The direction tells the converter whether your number is cups or fluid ounces. A negative amount is read as zero.

1. Convert through the cubic metre. Each unit is stored as its exact size in cubic metres, built from the US gallon of 231 cubic inches and the international inch of 2.54 cm. The cup is the gallon divided by 16 and the fluid ounce is the gallon divided by 128. Converting multiplies by the size of the unit you start in and divides by the size of the unit you want, so the ratio between a cup and a fluid ounce comes out as exactly 8.

1. Give the same volume in other units. The same conversion produces millilitres (the cup is 236.5882365 mL), US tablespoons (16 to the cup) and label cups of exactly 240 mL, the size defined for serving sizes in 21 CFR 101.9.

1. Weigh it as water. The volume is multiplied by the density of pure, air-free water at 20 °C from the CIPM formula, 998.2067 kg per cubic metre, and the mass is converted to avoirdupois ounces.

1. Round for display only. The arithmetic runs at 34 significant digits and is rounded half up when shown: fluid ounces to four places, cups to six, millilitres to two, tablespoons and label cups to four, water weight to three. For any input with up to two decimal places the fluid ounce and cup figures are exact at those precisions.

The default, 1 cup to fluid ounces:

1. Fluid ounces: 1 × 8 = 8 fl oz.
2. Millilitres: 236.59 mL. Tablespoons: 16 tbsp.
3. In 240 mL label cups: 0.9858, a little under one label cup.
4. As water: 8.33 oz by weight, slightly more than the 8 fluid ounces of volume.

Three quarters of a cup: 0.75 × 8 = 6 fl oz, which is 12 tablespoons or 177.44 mL.

Going the other way, 5 fluid ounces to cups: 5 ÷ 8 = 0.625 cups, which is half a cup plus two tablespoons. And 40 fluid ounces is 40 ÷ 8 = 5 cups, or 1,182.94 mL.

Every row comes from the converter's own reference table, which runs to 16 cups. Four cups is a quart and 16 cups is a gallon.

A US cup holds 8 US fluid ounces. That is the answer for water, milk, stock, oil or any other liquid measured by volume, because a fluid ounce is a volume. It is also the answer for a dry ingredient measured in a cup, but only as a volume: 8 fluid ounces of flour does not weigh 8 ounces.

The word "ounce" covers two different things. A fluid ounce is a volume, one 128th of a US gallon. An ounce on a kitchen scale is a weight, one sixteenth of a pound. They only line up for something about as dense as water, and even then not exactly: the water card shows that a cup of water weighs 8.33 oz, not 8.

For anything else, a cup by volume and its weight in ounces are far apart. Flour is much lighter than water, so a cup of it weighs well under 8 ounces; honey is heavier. If a recipe says "8 oz of flour", it wants a weight and you need a scale or a density, not this converter. The grams to teaspoons and cups converter on this site uses measured USDA weights for common ingredients.

This page uses the US customary cup, 236.5882365 mL, the one on American measuring cups and in American recipes. Two other cups are in common use:

• The US label cup, exactly 240 mL, used for serving sizes on Nutrition Facts panels. It is slightly bigger than a customary cup, which is why one customary cup reads as 0.9858 label cups.
• The imperial or metric cup in British, Australian and Canadian recipes. Those use different sizes and different fluid ounces, and this converter does not cover them. The UK pint, for example, is defined in the Weights and Measures Act 1985 as 0.56826125 litres, noticeably more than the US pint of two cups.

• Imperial measures. Only US customary cups and fluid ounces are converted. A British recipe's cups and fluid ounces are different sizes.
• Weight ounces. The converter turns volume into volume. The water weight card is the only weight it gives, and it is for pure water at 20 °C.
• How you fill the cup. A liquid measuring cup read at eye level and a dry cup levelled with a knife hold the same volume on paper, but heaped, packed or shaken ingredients do not.
• Fractions typed as fractions. The box takes decimals. A third of a cup has no exact decimal, so typing 0.333 gives a figure a hair under the true amount. Type more threes for a closer answer.

• Weighing a cup of flour as 8 ounces. This is the classic mistake. Eight fluid ounces of flour weighs far less than 8 ounces.
• Mixing US and UK recipes. A British recipe that asks for 10 fl oz is using imperial fluid ounces. Converting it with US factors gives a slightly different amount.
• Rounding the label cup to a cup. Most of the time the small gap does not matter, but scaling a recipe up by twenty makes it worth noticing.
• Reading "c" and "C". Older recipes write cups as "c" or "C"; they mean the same thing, a US cup.

• NIST Handbook 44, Appendix C, General Tables of Units of Measurement: the US gallon, cup and fluid ounce. nist.gov/pml/owm/nist-handbook-44-current-edition
• NIST Special Publication 811, Guide for the Use of the International System of Units (2008), Appendix B: conversion factors to SI. nist.gov/pml/special-publication-811
• eCFR, 21 CFR 101.9(b)(5)(viii), Nutrition labeling of food: the 240 mL cup and 30 mL fluid ounce used for serving sizes. ecfr.gov/current/title-21/chapter-I/subchapter-B/part-101/subpart-A/section-101.9
• UK legislation, Weights and Measures Act 1985, Schedule 1: the imperial pint. legislation.gov.uk/ukpga/1985/72/schedule/1
• Metrologia 38 (2001) 301-309, Tanaka et al., Recommended table for the density of water between 0 °C and 40 °C (CIPM formula). doi.org/10.1088/0026-1394/38/4/3