Cups to Oz Calculator
Convert between cups and fluid ounces — US, imperial, and metric. Exact NIST and UK statutory factors, bidirectional, no rounding tricks.
1 US cups (customary, 8 fl oz) =
8
Converted via the millilitre pivot — 236.5882365 mL per us_cup, 29.5735295625 mL per us_floz. US cup = 8 US fl oz exact (1/16 US gal, NIST SP 1038), US fl oz = 29.573 529 5625 mL exact, imperial fl oz = 28.413 0625 mL exact (UK W&M Act 1985), US legal cup = 240 mL exact (21 CFR 101.9), metric cup = 250 mL exact (AS 1349).
How to use this calculator
Type a value, choose the cup type (or fluid ounce type) in "From", and the unit you want in "To". The result updates instantly. Switching the From and To selects flips the conversion direction, so it works as an oz-to-cups calculator too.
How the calculation works
Every unit converts via an intermediate value in millilitres. The factors are exact: 1 US gallon = 231 cubic inches (NIST SP 1038), so a US fluid ounce (1/128 gallon) is 29.573 529 5625 mL and a US customary cup (1/16 gallon) is exactly 8 US fluid ounces = 236.588 2365 mL. The US legal cup used on nutrition labels is 240 mL exactly (21 CFR 101.9), which is about 8.115 US fl oz. A metric cup (Australia, New Zealand, Canada) is 250 mL exactly, about 8.454 US fl oz. An imperial fluid ounce is 1/160 of an imperial gallon = 28.413 0625 mL exactly (UK Weights and Measures Act 1985), and an imperial cup is exactly 10 imperial fluid ounces.
Worked example
2 US cups → US fluid ounces: 2 × 236.588 2365 mL = 473.176 mL ÷ 29.573 529 5625 mL/fl oz = 16 US fl oz. The shortcut cups × 8 works because a US customary cup is defined as exactly 8 US fluid ounces. For a metric cup the shortcut fails: 2 × 250 mL = 500 mL ÷ 29.573 529 5625 = 16.91 US fl oz, not 16.
Frequently asked questions
How many ounces are in a cup?
A US customary cup — the cup in American recipes — is exactly 8 US fluid ounces. A US legal cup (nutrition labels, 240 mL) is about 8.12 US fl oz, a metric cup (250 mL) is about 8.45 US fl oz, and an imperial cup is exactly 10 imperial fluid ounces (about 9.61 US fl oz).
Are fluid ounces the same as ounces on my kitchen scale?
No — this is the biggest source of cup-to-oz mistakes. Fluid ounces measure volume; the ounces on a scale measure weight. They only line up for water-like liquids (1 US fl oz of water weighs about 1.04 oz). A cup of flour is 8 fl oz by volume but weighs only about 4.25 oz. To convert cups of a dry ingredient to weight, you need that ingredient’s density, not this calculator.
Is a US fluid ounce the same as a UK (imperial) fluid ounce?
No. A US fluid ounce is 29.5735 mL and an imperial fluid ounce is 28.4131 mL — the US one is about 4% larger. One imperial fl oz = 0.96076 US fl oz. The calculator offers both so you can convert between the systems exactly.
Which cup should I use for an American recipe?
Use the "US cups (customary)" option — that is the cup used in almost every American cookbook, and it converts to fluid ounces by a clean × 8. The 240 mL legal cup only appears on packaged-food nutrition panels and is not the cup recipes assume.
How many cups is 16 oz?
16 US fluid ounces is exactly 2 US customary cups. In metric cups it is about 1.89 cups (473.18 mL ÷ 250 mL), and in imperial fluid ounces 16 US fl oz is about 16.65 imp fl oz.
How accurate is this converter?
Conversions use the exact NIST and UK statutory factors and run in full floating-point precision. Display rounding is the only source of imprecision, and that is at the sub-millilitre level.