How the Oz to Cups Converter Works
The widget on this page handles three slightly different cup definitions — US standard, UK Imperial, and Metric — because that's the actual mess every cook hits when using a recipe from a different country. Pick the system, enter your value in either fluid ounces or cups, and the other side updates instantly.
For US recipes, the standard is 8 US fluid ounces per cup. That's the default. UK Imperial uses 10 Imperial fluid ounces per cup (slightly larger because Imperial fl oz are slightly smaller). The Metric cup is defined as exactly 250 mL, which works out to about 8.45 US fluid ounces.
12 ÷ 8 = 1.5 cups.
Now if a UK recipe calls for 12 Imperial fl oz of milk, that's 12 ÷ 10 = 1.2 UK cups. The number changes because the cup itself is bigger in the UK system.
Quick Reference — US Cup ↔ Fluid Ounces
| Cups | Fluid ounces (US) | Milliliters (approx.) |
|---|---|---|
| 1/4 cup | 2 fl oz | 59 mL |
| 1/3 cup | 2.67 fl oz | 79 mL |
| 1/2 cup | 4 fl oz | 118 mL |
| 2/3 cup | 5.33 fl oz | 158 mL |
| 3/4 cup | 6 fl oz | 177 mL |
| 1 cup | 8 fl oz | 237 mL |
| 1.5 cups | 12 fl oz | 355 mL |
| 2 cups (1 pint) | 16 fl oz | 473 mL |
| 4 cups (1 quart) | 32 fl oz | 946 mL |
Why the Three Systems Exist
US. The US customary cup is 8 US fluid ounces, where the US fl oz is defined as 1/128 of a US gallon. The system was set in 1832 and hasn't changed.
UK Imperial. The UK Imperial cup, when used, is 10 Imperial fluid ounces — but the Imperial fluid ounce is slightly different from the US one (28.4 mL vs 29.6 mL). In modern UK cooking, the cup is rarely used at all — UK recipes overwhelmingly use grams and milliliters. When a UK recipe says "1 cup," it typically means the Metric 250 mL cup unless explicitly stated.
Metric. The Metric cup is defined as exactly 250 mL. Used in Australia, New Zealand, Canada (post-1970), and most countries that adopted SI units. The Metric cup is slightly larger than the US cup (250 mL vs 237 mL — about 5.5% difference), which is enough to throw off baking but doesn't matter much for soups or stews.
Dry Ounces vs Fluid Ounces — The Trap
An ounce can mean two completely different things in the kitchen:
- Fluid ounce (fl oz) — a unit of volume. 1 fl oz = ~29.6 mL. This converter is about fluid ounces.
- Dry ounce (oz) — a unit of weight. 1 oz = ~28.35 grams. NOT what this converter measures.
For water, 1 fl oz weighs almost exactly 1 oz, which is where the confusion comes from. But for flour, sugar, or anything with a different density, the two diverge dramatically. 1 cup of all-purpose flour is 8 fl oz (volume) but only ~4.5 oz (weight). 1 cup of granulated sugar is 8 fl oz (volume) and ~7 oz (weight). When converting weight measurements (grams, ounces of weight), use the Grams to Ounces converter, not this one.
Common Cooking Conversions
Butter. 1 stick of US butter = 8 tablespoons = 4 oz weight = 1/2 cup. Most US butter wrappers have tablespoon markings — use those instead of measuring.
Recipes scaled up or down. When doubling a recipe that calls for 1.5 cups of liquid: 1.5 × 2 = 3 cups, or 24 fl oz, or 710 mL. The math doesn't break — but the recipe might (cooking times, oven heat, pan size all scale non-linearly).
Reading international recipes. A British recipe saying "1 cup" usually means 250 mL (Metric cup). A 1950s American recipe means 8 US fl oz. Most modern American recipes also mean 8 US fl oz. When in doubt, weigh ingredients in grams instead of using volume — weight is unambiguous.
Related Tools
For converting milliliters and fluid ounces directly, use the Ml to Oz Converter. For weighing dry ingredients (flour, sugar, butter), the Grams to Ounces converter is the right choice. For broader unit conversion across length, weight, temperature, and more, see the Unit Converter.