A fluid ounce measures volume: 29.57 mL in the US, 28.41 mL in the UK. A “dry ounce” is just an ordinary ounce of weight, 28.35 g, the kind a kitchen scale reads. They’re different quantities, and they only roughly agree for water, where 1 US fluid ounce weighs about 1.04 ounces. For flour, a cup is 8 fluid ounces of volume but weighs only about 4.2 ounces.
Is there such a thing as a dry ounce? #
Not as an official unit. “Dry ounce” is kitchen shorthand for a weight ounce, used to tell it apart from a fluid ounce. The weight ounce is the avoirdupois ounce, 1/16 of a pound, exactly 28.349523125 g.
| Unit | Measures | Size | Defined as |
|---|---|---|---|
| US fluid ounce | Volume | 29.5735 mL | 1/128 US gallon |
| UK fluid ounce | Volume | 28.4131 mL | 1/160 imperial gallon |
| Ounce (“dry ounce”) | Weight | 28.3495 g | 1/16 pound |
| Troy ounce | Weight (precious metals) | 31.1035 g | 480 grains |
The US gallon is exactly 3.785411784 L and the imperial gallon exactly 4.54609 L (NIST SP 811), which is where both fluid ounces come from.
Why isn’t a cup of flour 8 ounces? #
Because 8 fluid ounces is a volume, and the weight of that volume depends on what fills it. Here’s one US cup (8 fl oz) of common ingredients by weight, using King Arthur Baking’s chart, except water, which uses its density:
| 1 cup (8 US fl oz) of… | Weighs (oz) | Weighs (g) |
|---|---|---|
| Water | 8.35 | 236.6 |
| Milk | 8.0 | 227 |
| Butter | 8.0 | 227 |
| Granulated sugar | 7.0 | 198 |
| Vegetable oil | 7.0 | 198 |
| All-purpose flour | 4.2 | 120 |
| Honey | 11.9 | 336 |
Only water-like liquids come out near 8 ounces. Flour weighs about half that, and honey about half again as much. That’s why “8 oz of flour” in a British or professional recipe means weight, nearly two US cups, not one.
The old saying “a pint’s a pound the world around” is the same approximation: a US pint of water (473 mL) weighs about 1.04 lb. It stops working for anything that isn’t water, and for the UK pint (568 mL), which weighs about 1.25 lb of water.
Are dry and liquid measuring cups different sizes? #
In the US, no. A dry measuring cup and a liquid measuring cup both hold 8 US fluid ounces. The difference is shape. Dry cups fill to the brim so you can level them with a knife. Liquid cups have a spout and markings below the rim so you can fill them without spilling.
Using the wrong one does introduce error. NIST’s culinary measurement tips note that using a dry measuring cup for liquids, or the reverse, “is a common way of introducing measurement errors into the cooking process.” For best accuracy, NIST recommends weighing ingredients on a kitchen scale.
What are US dry pints and dry quarts? #
The US does have separate dry measures, used for produce like berries and grain. They’re bigger than the liquid measures of the same name:
| Unit | Dry measure | Liquid measure |
|---|---|---|
| Pint | 550.6 mL | 473.2 mL |
| Quart | 1.101 L | 0.946 L |
| Gallon | 4.405 L | 3.785 L |
| Bushel | 35.24 L | — |
A dry pint is about 16% larger than a liquid pint. You’ll meet it on farm-stand berry baskets. Recipes almost never mean dry pints, and there’s no dry fluid ounce.
How do you read “oz” in a recipe? #
- Dry or solid ingredients: oz means weight. “8 oz chocolate” is 227 g on a scale.
- Liquids: oz usually means fluid ounces, especially in US recipes. “8 oz milk” is 1 cup.
- Packaged goods: labels say which. “NET WT 12 OZ” is weight. “12 FL OZ” is volume.
- British recipes: fluid ounces are imperial (28.41 mL), and dry amounts in ounces are weight.
Worked examples #
A recipe calls for 12 oz of chocolate chips. That’s weight: 340 g, which is about 2 cups using King Arthur’s 170 g per cup.
A recipe calls for 4 fl oz of cream. That’s volume: 1/2 US cup, 118 mL.
A British recipe calls for 10 fl oz of stock. Imperial fluid ounces: 284 mL, a half pint, about 1.2 US cups.
A bottle says 16.9 FL OZ. That’s 500 mL of volume. If it’s water, it weighs about 500 g, or 17.6 oz.
Converting both kinds of ounce on your phone #
Convert Units Calculator keeps the two kinds of ounce in separate categories so they can’t be confused: fluid ounces live in Volume (with US and UK versions from version 1.0.5), and weight ounces in Weight. When you need to cross from one to the other, its Cooking category (also 1.0.5) asks for the ingredient and converts cups, spoons or fluid ounces of it into grams or weight ounces.
For the individual conversions, see ml to oz for fluid ounces, grams to ounces for weight, and the cups to grams conversion chart for ingredient weights.
Frequently asked questions #
Is a dry ounce the same as a regular ounce? #
Yes. “Dry ounce” is an informal name for the ordinary weight ounce (28.35 g), used to distinguish it from the fluid ounce, which measures volume.
How many fluid ounces are in a cup? #
Eight US fluid ounces make one US cup (236.6 mL).
Does 8 oz always equal 1 cup? #
Only when “oz” means fluid ounces. By weight, a cup of an ingredient weighs 8 oz only if it has about the density of water. A cup of flour weighs about 4.2 oz and a cup of honey about 11.9 oz.
Is a fluid ounce of water an ounce by weight? #
Close. One US fluid ounce of water weighs about 1.04 oz (29.6 g). One UK fluid ounce of water weighs almost exactly 1 oz, because the imperial fluid ounce was originally based on the volume of an ounce of water.
What’s the difference between a dry pint and a pint? #
A US dry pint (550.6 mL) is about 16% bigger than a US liquid pint (473.2 mL). Dry pints are used for produce like berries. Recipes that say “pint” mean the liquid pint.