About

Mismeasuring liquid volume by even 0.5 fl oz in baking can collapse a cake's crumb structure or break an emulsion. The relationship is deceptively simple - 1 US customary cup = 8 US fl oz - but three competing cup standards exist globally. A US legal cup (240 mL) used on nutrition labels differs from the US customary cup (236.588 mL), and an Imperial cup (284.131 mL) yields 10 Imperial fl oz, not 8. This converter handles all three standards plus the metric cup (250 mL). It accepts fractional inputs like 1 3/4 because recipes rarely speak in decimals. Note: this tool converts fluid ounces (volume), not weight ounces. Flour, sugar, and water all weigh differently per cup.

Formulas

The core conversion between US customary cups and US fluid ounces is a linear scaling:

V_{fl oz} = V_cups × k

Where V_{fl oz} is the volume in fluid ounces, V_cups is the volume in cups, and k is the conversion factor for the selected cup standard.

Conversion factors by standard:

k_{US customary} = 8 US fl oz/cup

k_{US legal} = 8.115 US fl oz/cup

k_Imperial = 10 Imp fl oz/cup

k_Metric = 8.454 US fl oz/cup

The US legal cup is defined as exactly 240 mL by the FDA for nutrition labeling. The metric cup is exactly 250 mL, common in Australia, New Zealand, and Canada. The Imperial cup (284.131 mL) maps to 10 Imperial fluid ounces because the Imperial fluid ounce (28.413 mL) differs from the US fluid ounce (29.574 mL).

Fraction parsing follows the pattern: input 1 3/4 is parsed as 1 + 34 = 1.75 cups.

Reference Data

Cups (US Customary)	US Fluid Ounces	Milliliters	Tablespoons	Common Use
1/8	1	29.6	2	Splash of extract
1/4	2	59.1	4	Small sauce portion
1/3	2.667	78.9	5.33	Dry ingredient scoop
1/2	4	118.3	8	Standard recipe half
2/3	5.333	157.7	10.67	Batter recipes
3/4	6	177.4	12	Common baking measure
1	8	236.6	16	Standard cup
1 1/4	10	295.7	20	Soup base
1 1/2	12	354.9	24	Rice cooking water
1 3/4	14	414.0	28	Cake batter
2	16	473.2	32	1 US pint
2 1/2	20	591.5	40	Large batch mixing
3	24	709.8	48	Broth base
4	32	946.4	64	1 US quart
8	64	1892.7	128	1/2 US gallon
16	128	3785.4	256	1 US gallon

Frequently Asked Questions

A US customary cup equals 236.588 mL (8 US fl oz), derived from the US gallon. A US legal cup equals exactly 240 mL (8.115 US fl oz), defined by the FDA for nutrition labeling under 21 CFR 101.9. The difference is 3.4 mL per cup. Over 4 cups in a recipe, that accumulates to roughly 13.6 mL - nearly a tablespoon. For precision baking, know which standard your recipe uses.

The Imperial fluid ounce is smaller than the US fluid ounce: 28.413 mL versus 29.574 mL. An Imperial cup holds 284.131 mL, which divides evenly into 10 Imperial fluid ounces. If you apply a US recipe's 8 oz ratio to Imperial measures, you will underfill by roughly 20%. Always confirm which system your recipe follows.

Fluid ounces only. A fluid ounce is a unit of volume (29.574 mL US). A weight ounce (avoirdupois) is 28.35 g. One cup of water weighs approximately 8.345 weight ounces, close to 8 fl oz by coincidence. One cup of all-purpose flour weighs only about 4.4 weight ounces despite occupying 8 fl oz of volume. Never interchange the two in recipes.

Yes. The parser accepts whole numbers (2), decimals (1.5), simple fractions (3/4), and mixed numbers (1 3/4). The fraction 3/4 is converted to 0.75 before applying the conversion factor. Division by zero in a fraction (e.g., 3/0) is caught and returns an error.

Australia, New Zealand, and Canada use the metric cup of exactly 250 mL. This is 8.454 US fl oz, about 5.7% larger than a US customary cup. A recipe from an Australian cookbook calling for 2 cups of milk expects 500 mL, not 473 mL. Select the Metric standard in this converter when working with such recipes.

Liquids expand when heated. Water at 100 °C occupies roughly 4% more volume than at 4 °C. The standard definitions of cups and fluid ounces assume room temperature (approximately 20 °C). For most cooking this is negligible, but in scientific or commercial food production, measure liquids at a consistent temperature. This tool does not apply thermal expansion corrections.