US vs UK fluid ounce
The fluid ounce is a unit of volume, not weight. The US customary system defines 1 US fluid ounce as exactly 29.5735 ml. The UK imperial system, used in British recipes, defines 1 imperial fluid ounce as 28.4131 ml. The difference is small, but it compounds for larger volumes — a US pint is 473 ml, an imperial pint is 568 ml.
Quick reference
- 1 US fl oz = 29.5735 ml
- 1 UK (imperial) fl oz = 28.4131 ml
- 1 US cup = 8 US fl oz = 236.6 ml
- 1 metric cup = 250 ml
- 1 US pint = 473.2 ml; 1 UK pint = 568.3 ml
FAQ
Why does my measuring jug show 250 ml = 8 oz? Many jugs round 1 cup to 250 ml for convenience. The exact value is 236.6 ml.
Are dry and fluid ounces the same? No. A dry ounce is 28.35 g (mass). A fluid ounce is 29.57 ml (volume). Recipes that say "8 oz of flour" usually mean dry ounces.