Why cups-to-grams isn't a fixed ratio
A cup measures volume, a gram measures mass — the two only translate into each other via the ingredient's density, and density varies a lot between ingredients. A cup of flour weighs roughly 125g when spooned lightly into the cup and leveled off, but can weigh 156g or more if you scoop directly from the bag and pack it down without realizing — nearly a 25% difference from measuring technique alone, before you even change ingredients. A cup of granulated sugar weighs about 200g; a cup of honey weighs about 340g, since honey is far denser than a dry, aerated ingredient like flour. This is exactly why baking recipes that specify weight (grams) are more reliable and reproducible than ones that specify volume (cups) — weight removes the "how did you measure it" variable entirely.
Common measuring mistakes
The single biggest source of error is scooping flour directly from the bag or canister with the measuring cup — this compacts the flour and can add 20-25% more than the recipe intended. The correct method: fluff the flour first, spoon it into the measuring cup without pressing down, then level off the top with a straight edge. Brown sugar is the opposite case — it's meant to be packed firmly into the cup (recipes usually say "packed" explicitly for this reason), since brown sugar's moisture content means unpacked measurements are inconsistent and too light.
Quick reference chart
| Ingredient | 1 cup | ½ cup | ¼ cup |
|---|---|---|---|
| All-purpose flour (spooned) | 125g | 62.5g | 31g |
| Granulated sugar | 200g | 100g | 50g |
| Butter | 227g | 113.5g | 56.75g |
| Brown sugar (packed) | 220g | 110g | 55g |
FAQ
Is 1 cup always 240g? No — 1 cup of water is close to 240g, but that's specific to water's density. Most baking ingredients are lighter (flour, sugar) or heavier (honey) than water by volume.
Does the ingredient's temperature matter? For butter, yes — measuring melted butter by volume gives a different weight than measuring solid butter, since melted butter is denser per cup. The calculator above assumes solid/room-temperature butter, the standard baking convention.