Converting Cooking Measurements: Spoons, Cups and Ounces

Volume and weight are different things

Recipes mix two kinds of measurement. Volume describes how much space an ingredient takes up: teaspoons, tablespoons, fluid ounces, cups, millilitres. Weight (strictly, mass) describes how much of it there is: ounces, pounds, grams. Converting within one kind is exact arithmetic. Converting between the two is not, because it depends on the ingredient.

A cup of flour, a cup of honey and a cup of water fill the same space but weigh very different amounts. That is why a unit converter, including the volume and mass tabs of this one, converts volume to volume and mass to mass, but never a cup to a gram. For that you need the ingredient’s density, which varies with how it is packed and sifted.

The ounce adds to the confusion. A fluid ounce measures volume; an ounce on its own measures weight. Check which one a recipe means before you convert.

The US kitchen ladder

US recipes use a chain of units in which each step is a simple multiple of the one below:

• 3 teaspoons = 1 tablespoon
• 2 tablespoons = 1 fluid ounce
• 8 fluid ounces = 1 cup (so 16 tablespoons or 48 teaspoons)
• 2 cups = 1 pint
• 2 pints = 1 quart
• 4 quarts = 1 gallon

These ratios let you convert by counting. Three quarters of a cup is 12 tablespoons, because 0.75 × 16 = 12. One and a half tablespoons is 4½ teaspoons. Half a cup is 4 fluid ounces. If you have lost a measuring cup, a tablespoon and a little patience will do.

Exact values in millilitres

The US gallon is defined as exactly 231 cubic inches, which is 3.785411784 litres. Every smaller unit follows from it by division:

• 1 fluid ounce = 29.5735295625 mL
• 1 tablespoon = 14.78676478125 mL
• 1 teaspoon = 4.92892159375 mL
• 1 cup = 236.5882365 mL
• 1 pint = 473.176473 mL

For everyday cooking these round to roughly 5 mL, 15 mL, 30 mL and 237 mL. US nutrition labelling uses its own rounded convention: the FDA guidance states that a teaspoon means 5 mL, a tablespoon 15 mL, a fluid ounce 30 mL and a cup 240 mL. Those are labelling values, not the true sizes of the measures.

The gap is small for a spoonful and noticeable for a large quantity. Four cups is 946.35 mL by the exact definition, but 960 mL by the labelling convention.

Worked examples

Cups to millilitres. A recipe asks for ¾ cup of milk: 0.75 × 236.5882365 = 177.4 mL. Measuring 175 mL or 180 mL will make no practical difference.

Millilitres to cups. A metric recipe calls for 250 mL of stock: 250 ÷ 236.5882365 = 1.057 cups. That is one cup plus about 1 tablespoon (0.057 × 16 = 0.9 tablespoons).

Litres to cups. One litre is 1,000 ÷ 236.5882365 = 4.23 US cups, or a little over a quart (a quart is 946.35 mL).

Mixed amounts. A recipe calling for 2 tablespoons and 1 teaspoon is 7 teaspoons in total, which is 7 × 4.92892 = 34.5 mL. Convert everything to the smallest unit first, add, then convert the total.

Type the amount into a converter, choose the units and read the result with as many decimal places as you need; for kitchen use, two decimals is plenty.

Weight units in the kitchen

The pound is defined as exactly 0.45359237 kilograms, so 1 lb = 453.59237 g. An ounce is one sixteenth of that, 28.349523125 g. So 8 oz is 226.8 g and 1 lb is about 454 g. These are exact, ingredient-independent conversions.

A common US ingredient, butter, is sold in sticks. One stick is ½ cup, or 8 tablespoons, or 4 oz — about 113 g. The identical quantity in three units is a handy check on your arithmetic: 8 tablespoons × 14.787 mL ≈ 118 mL, half a cup.

Going between cups and grams needs an ingredient figure. One widely used baking chart lists 1 cup of all-purpose flour as 120 g and 1 cup of granulated sugar as 198 g; other sources give different figures, because flour packs differently depending on how it is scooped. Treat any such figure as an estimate.

Getting accurate results

Keep full precision until the end. If you round 29.57 to 30 and then multiply by eight, you add a visible error; multiply first, round last.

Level dry ingredients with a straight edge, and read liquid measures at eye level on a flat surface. Heaped or packed spoonfuls can differ from level ones by a large margin.

Round to the precision the task deserves. A soup can absorb an extra tablespoon. Bread and cake are more sensitive, because the ratio of flour to liquid matters, so a scale and gram quantities give more consistent results than cups.

Measuring spoons and cups differ between countries: the Australian tablespoon, for example, is 20 mL and holds four teaspoons, while most other places use 15 mL and three. Spoons from the cutlery drawer are not measuring spoons. Never use kitchen conversions for medicines; follow the label or a pharmacist’s instructions. For anything safety-critical, such as preserving food, use the figures in the original source.