Volume or weight
| Unit | Measures | Size |
|---|---|---|
| US fluid ounce (fl oz) | Volume | 29.57 mL |
| UK (imperial) fluid ounce | Volume | 28.41 mL |
| Ounce (oz) | Weight | 28.35 g |
US food labels round these to 30 mL for a fluid ounce and 28 g for an ounce.
A US cup holds 8 fluid ounces. But 8 ounces of flour by weight is 227 g, which is nearly two cups at King Arthur’s 120 g per cup, because flour is much lighter than water.
Which a recipe means
Liquids are usually measured in fluid ounces, and dry ingredients like flour, sugar and chocolate in ounces by weight. When a recipe just says “oz” for a solid ingredient, weigh it.
Two more catches
- US and UK pints differ. A US pint is 16 US fluid ounces (473 mL); a UK pint is 20 UK fluid ounces (568 mL).
- Precious metals use a heavier troy ounce of 31.1 g, not the kitchen ounce.