Cooking Conversions: Cups to Grams, Fahrenheit to Celsius

A recipe says 2 cups of flour, your scale measures grams, and your oven speaks Fahrenheit while the recipe says 180 Celsius. Cooking conversions trip up even confident cooks, because volume and weight are not interchangeable — and the difference between them is exactly why one person's cake rises and another's does not.

Why weight beats volume

A cup is a measure of space, not of amount. A cup of flour can weigh anywhere from 120 to 150 grams depending on how tightly it was packed into the cup, which means two cooks following the same recipe can use up to 25 percent different amounts of flour. That is the difference between a tender crumb and a brick. A kitchen scale removes the variable entirely: 250 grams of flour is 250 grams of flour, no matter who measures it.

This is why professional bakers work in grams and why most of the world's recipes are written that way. If you bake more than occasionally, a cheap digital scale is the single best upgrade you can buy. For everything else — soups, sauces, salads — volume measurements are fine, because precision matters less.

The tables every baker needs

These are the conversions that cover most recipes. Note that dry ingredients differ because they have different densities — a cup of sugar weighs far more than a cup of flour.

• Flour: 1 cup = 120 g; 1 tablespoon = 8 g
• Granulated sugar: 1 cup = 200 g; 1 tablespoon = 12.5 g
• Brown sugar (packed): 1 cup = 220 g
• Butter: 1 cup = 227 g (one US stick = 113 g = 8 tablespoons)
• Cocoa powder: 1 cup = 100 g
• Rolled oats: 1 cup = 90 g
• Honey and syrups: 1 cup = 340 g
• Water and milk: 1 cup = 240 ml = 240 g

Volume conversions are simpler because they are exact: 1 tablespoon = 3 teaspoons, 1 cup = 16 tablespoons, 1 cup = 240 ml, 1 pint = 2 cups, 1 quart = 4 cups, and 1 gallon = 16 cups. Memorize the tablespoon-to-teaspoon rule and the cup-to-millilitre rule and you can convert most recipes on the fly.

Fahrenheit to Celsius (and back)

Oven temperatures are the most common conversion in cooking, and the formula is straightforward: Celsius = (Fahrenheit - 32) x 5/9, and Fahrenheit = Celsius x 9/5 + 32. In practice, you only need the handful of temperatures that recipes actually use:

• 325 F = 165 C — slow baking, custards, cheesecakes
• 350 F = 175 C — the default for most cakes and cookies
• 375 F = 190 C — roasting vegetables, crisping pastry
• 400 F = 200 C — roasting meat, pizza
• 425 F = 220 C — high-heat roasting, bread
• 450 F = 230 C — pizza ovens, searing

Rounding to the nearest 5 or 10 degrees is fine — home ovens vary by more than that anyway. What matters is not confusing the two scales: a cake baked at 350 C instead of 350 F is a fire hazard, and this mistake happens more often than anyone admits.

Worked example: converting a US recipe to metric

Take a cookie recipe that calls for 2 1/4 cups of flour, 1 cup of butter, 3/4 cup of sugar, and a 350 F oven. Converting: 2 1/4 cups of flour is 2.25 x 120 = 270 g. One cup of butter is 227 g, or two sticks. Three-quarters of a cup of sugar is 0.75 x 200 = 150 g. The oven goes to 175 C. The converted recipe reads 270 g flour, 227 g butter, 150 g sugar, 175 C — and it will bake exactly the same, because the amounts are identical, just measured properly.

Scaling works the same way. Doubling a recipe means doubling every ingredient, including salt, baking powder, and yeast — but not necessarily the cooking time. A doubled cake in a larger pan needs roughly 25 percent more time, not double, and you should check it early rather than trusting the clock.

The mistakes that ruin recipes

• Scooping flour straight from the bag. This packs it down and adds up to 30 percent extra. Spoon flour into the cup and level it off, or better, weigh it.
• Treating fluid ounces and weight ounces as the same. A fluid ounce measures volume; an ounce measures weight. They only match for water. Eight fluid ounces of honey weighs about 12 ounces.
• Using a dry measuring cup for liquids. You cannot fill it to the brim without spilling, so you under-measure. Use a clear jug with a spout for liquids.
• Converting cups to grams with one universal number. There is no single "cup to grams" conversion — it depends on the ingredient. Any chart that gives one number for all ingredients is wrong.

Frequently asked questions