Cups to Grams: Why Your Baking Math Is Off
A cup is a volume measure; grams are mass. The same cup of flour weighs far less than a cup of sugar. Learn why density breaks naive cup-to-gram swaps, plus a per-ingredient converter.
By The UnitFig Editorial Team · August 29, 2026 · reviewed against NIST and SI reference sources
Volume is not mass
A US cup is 240 mL of space. What fits in that space depends on how heavy the ingredient is (its density). One cup of all-purpose flour is about 120 g; one cup of granulated sugar is about 200 g. A flat "cups × 240 = grams" formula is wrong by design.
Mistake 1: assuming one universal cup weight
Using a single grams-per-cup number for every ingredient is the top baking error. Flour, sugar, brown sugar (packed), and cocoa differ by 40–80 g per cup. Scale recipes by ingredient, not by a global factor.
Mistake 2: packed vs spooned measuring
The reference values assume spooned-and-leveled cups. Pressing flour into the cup (packed) adds 20–30% more mass, throwing off the whole recipe. Weigh with a scale for repeatable results.
Frequently Asked Questions
How many grams in one cup of flour?
About 120 g for all-purpose flour, spooned and leveled. Brown sugar packed is ~220 g per cup.
Can I just multiply cups by 240?
Only if you mean milliliters, not grams. Converting to grams requires the ingredient’s density.
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Quick Summary
Never treat a cup as a fixed number of grams — its mass depends on ingredient density and how it was scooped. Use the per-ingredient converter or a kitchen scale; spoon-and-level, do not pack, when using cups.
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Disclaimer
Unit conversions on this site use internationally recognized, fixed conversion factors (for example, 1 inch = 2.54 cm, 1 pound = 0.45359237 kg, 1 °F = (°C × 9/5) + 32). They are provided for general, informational, and educational use. For applications where accuracy is critical — such as medical dosing, engineering, scientific research, trade, or legal compliance — always verify results against authoritative sources such as the U.S. National Institute of Standards and Technology (NIST) and the official International System of Units (SI) brochure, and follow any applicable local standards.
Exact Constants & Authoritative Sources
Every conversion on this page uses the fixed, internationally agreed constants below — drawn from NIST and the SI Brochure. No values are estimated or rounded as if exact. See the full list on our Sources & Standards page.
- EXACT1 US gallon (gal) = 3.785411784 litres (exact, 231 in³)
- EXACT1 US fluid ounce (fl oz) = 29.5735295625 mL (exact, 1/128 gal)
- EXACT1 US cup = 236.5882365 mL (exact, 8 fl oz)
- EXACT1 US pint (pt) = 473.176473 mL (exact, 16 fl oz)
- EXACT1 US quart (qt) = 946.352946 mL (exact, 32 fl oz)
- EXACT1 litre (L) = 1000 millilitres (definition)
Common Pitfalls & How to Avoid Them
US vs. Imperial (UK) cups
A US cup is 236.59 mL, but a UK/metric cup is 250 mL and an Imperial cup is ~284 mL. Recipes from different countries are not interchangeable drop-in.
Fluid ounce is volume, not mass
A US fl oz is 29.57 mL of volume. 1 fl oz of water ≈ 29.57 g, but 1 fl oz of honey or oil weighs more. Do not treat fluid ounces as grams.
Teaspoon/tablespoon sizes differ
1 US tbsp = 14.7868 mL; 1 US tsp = 4.92892 mL. Metric measuring spoons are 15 mL and 5 mL — close but not exact; for baking precision use weighed grams.
A unit-conversion reference site has no manufacturer-specific or device calibration parameters, so "layered tuning" does not apply here. The only real error-handling is input validation: the converter rejects non-numeric, empty, or out-of-range entries and shows a clear message, then falls back to exact constants above. No estimated or rounded figures are ever presented as exact.
Authoritative sources for this page
- NIST (U.S. National Institute of Standards and Technology) — NIST SP 330 — The International System of Units (SI), 2019 edition
- BIPM (International Bureau of Weights and Measures) — SI Brochure — The International System of Units (9th edition)
Last Updated 2026 | This article was reviewed for accuracy