A Practical Guide to Kitchen Measurement Conversions

"How many grams in a cup?" doesn't have one answer. It has a different answer for every ingredient. A cup of flour and a cup of honey take up the exact same volume but weigh nowhere near the same amount, which is the single most common source of a recipe going wrong after a unit conversion: treating volume and weight as if they're always interchangeable, when the only thing connecting them is a number that changes per ingredient.

Volume and weight are only related through density

Volume measures how much space something takes up. Weight measures mass. The two are only related through density (mass ÷ volume), and density varies enormously between ingredients: flour is light and full of air pockets, honey is thick and dense, butter sits in between. That's why "convert 1 cup to grams" is an incomplete question until you specify what's in the cup. Our Cooking Measurement Converter handles this by looking up each ingredient's actual density before converting, rather than applying one fixed cups-to-grams number to everything.

Here's what 1 US cup of several common baking ingredients actually weighs:

Honey weighs almost three times as much as flour for the identical cup of volume (340 g vs. 120 g). Nothing about the cup changed, only what's filling it. This is also why a kitchen scale is more reliable than measuring cups for baking specifically: weight doesn't care how tightly flour got packed into the cup or whether it was leveled off, so it removes an entire category of measuring error that volume can't.

The volume units themselves, and how they nest

Within volume, US customary units nest inside each other at fixed ratios that don't depend on the ingredient at all:

These ratios are exact regardless of what's being measured. 16 tablespoons of honey and 16 tablespoons of flour are still both exactly 1 cup by volume, even though their weights differ the same way the table above shows. It's only the moment you convert to weight (grams or ounces) that the specific ingredient starts to matter.

A worked substitution example

Say a recipe calls for 1½ cups of granulated sugar, and you want to know the weight to portion it on a scale instead. At 200 g per cup, 1.5 cups comes to 300 g. If you're substituting brown sugar for part of that sugar (packed brown sugar is denser, at 220 g per cup), swapping in cup-for-cup measurements is fine (1.5 cups of brown sugar is still 1.5 cups by volume), but if you're trying to match the sugar by weight instead (say, converting a weight-based recipe to volume, or vice versa), you can't just reuse the granulated sugar's 200 g figure for brown sugar; you need brown sugar's own 220 g-per-cup density, or the substitution will be off by about 10%.

US customary vs. US legal vs. imperial: three different "cups"

There's an additional wrinkle that trips up conversions between countries: "a cup" isn't even a single fixed volume worldwide. The US customary cup used in American recipes and by this converter is 236.588 mL. US nutrition labels use a separate, rounded "US legal cup" of exactly 240 mL for labeling purposes. The UK/imperial cup (less commonly used today, but still found in older British recipes) is 284.131 mL, about 20% larger than the US customary cup. Following a British recipe with American measuring cups, or vice versa, without accounting for this difference is a real, common source of a recipe coming out wrong that has nothing to do with ingredient density at all. The same gap applies to fluid ounces: a US fluid ounce is 29.5735 mL, while an imperial fluid ounce is 28.4131 mL.

When you don't need density at all

Converting between two volume units (cups to tablespoons, milliliters to fluid ounces) or two weight units (grams to ounces) never requires knowing the ingredient, since both sides of that conversion are the same kind of measurement. It's only volume-to-weight or weight-to-volume conversions (the ones that actually matter for portioning ingredients on a scale) where density enters the picture. If you just need a straight unit conversion with no ingredient involved (say, converting a recipe's Celsius oven temperature or a package weight in ounces to grams), our general-purpose Unit Converter handles that without needing an ingredient selected at all.