How many fluid ounces are in a cup?

In the US system, 1 cup equals exactly 8 US fluid ounces. In the UK (imperial) system, 1 metric cup equals approximately 8.799 UK fluid ounces.

Why are US and UK fluid ounces different?

The US fluid ounce is based on the US customary system (approximately 29.5735 mL), while the UK (imperial) fluid ounce is slightly smaller (approximately 28.4131 mL). Because both the cup size and the fluid ounce size differ, the ratio between them varies by system.

What is a "cup" exactly?

In the US, 1 cup is exactly 236.588 mL. In Australia and Canada, 1 metric cup is 250 mL. This converter uses the US cup (236.588 mL) for US fl oz and the metric cup (250 mL) for UK fl oz calculations, which matches common culinary usage.

Can I convert fluid ounces back to cups?

Yes. Click the swap button below the result to reverse the conversion. Enter the number of fluid ounces and get the equivalent in cups for both US and UK systems.

Is 1 cup always 8 fl oz?

In the US customary system, yes — 1 cup is exactly 8 US fluid ounces. This is a fixed definition. The UK does not use "cup" as an official unit, but recipes using UK measurements often adopt the 250 mL metric cup, which is roughly 8.799 UK fluid ounces.

Cups to Fluid Ounces Converter

Name: Cups to Fluid Ounces Converter
Availability: InStock
Author: Nham Vu

Enter a value in cups and instantly see the equivalent in US and UK fluid ounces.

Enter Volume in Cups

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Enter cups above to see the conversion.

US Fluid Ounces 1 cup = 8 fl oz

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UK Fluid Ounces (Imperial) 1 cup ≈ 8.799 fl oz

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Quick reference

Cups	US fl oz	UK fl oz

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Summary

Enter a value in cups and instantly see the equivalent in US and UK fluid ounces.

How it works

Enter the number of cups in the input field.
The converter calculates US fluid ounces (1 cup = 8 fl oz) in real time.
It also calculates UK fluid ounces (1 cup = 8.799 fl oz) simultaneously.
Use the swap button to convert fluid ounces back to cups.
Common preset values let you convert quickly without typing.

Use cases

Scale up or down a recipe that lists volumes in cups.
Convert a US recipe to UK measurements when cooking abroad.
Double-check liquid measurements when a measuring cup is unavailable.
Understand beverage serving sizes listed in cups vs. fluid ounces.
Convert bulk ingredient quantities for food production or catering.
Verify nutrition label serving sizes expressed in different units.

Frequently Asked Questions

Last updated: 2026-07-01 · Reviewed by Nham Vu