How We Calculate
Where every number on Cooking Measure comes from, how we convert between cup sizes, and how results are rounded.
45 ingredients42 USDA, 3 King ArthurChecked
One data file for the whole site
Every ingredient weight lives in a single file, stored as grams per US customary cup. The grams to cups converter, the grams per cup table and the flour page all read from it, so a number cannot say one thing on one page and something else on another. The file is generated by a script from the source data below; no weight is typed in by hand.
Where the ingredient weights come from
- USDA FoodData Central (SR Legacy release): 42 ingredients. We use the food's published "1 cup" portion weight, choosing the portion that matches how the ingredient is sold or measured (for example "cup, packed" for brown sugar, "cup, shredded" for cheddar). Each row in our tables links to the USDA record number. On November 15, 2026 we re-checked all 42 rows against USDA's live FoodData Central API; none differed.
- King Arthur Baking ingredient weight chart: 3 ingredients (cake flour, almond flour, coconut flour). We use it where USDA has no usable cup weight, or where USDA's cup was measured in a way bakers don't use (USDA's cake flour cup is dipped into the bag). Where King Arthur lists a half or quarter cup, we scale it to one cup.
Where both sources list an ingredient, the tables show both and we pick one for the whole site. If neither gives a per-cup weight, the ingredient isn't on the site. That is why there is no figure for sifted all-purpose flour.
Cup sizes
| Cup | Volume | Definition |
|---|---|---|
| US customary cup | 236.5882 ml | NIST Handbook 44 (2024), Appendix C: 1 measuring cup = 8 fl oz = 1/16 gallon; 1 gallon = 231 cubic inches exactly |
| US legal cup (nutrition labels) | 240 ml | FDA 21 CFR 101.9(b)(5)(viii): 1 cup = 240 mL |
| Metric cup (Australian Standard; AU / NZ recipes) | 250 ml | Standards Australia AS 1325 (metric measuring cups and spoons): 1 cup = 250 mL |
250 ml cups are also common in Canadian recipes, but we found no official Canadian standard that defines the cup, so we treat it as a recipe convention, not a standard.
The US customary cup is 8 US fluid ounces, one-sixteenth of a US gallon of 231 cubic inches, which works out to 236.5882365 ml. For the US legal and metric cups we multiply the US-cup weight by the ratio of the volumes. For liquids this is exact. For dry ingredients it is a close estimate, because the weight also depends on how the cup is filled.
Rounding
- Cups: Cup fractions are rounded to the nearest ⅛ cup (⅓ and ⅔ are used when closer); the decimal in brackets is the value to 2 places, and ≈ marks a rounded fraction. When the fraction and the decimal differ, the fraction gets a ≈ sign. Example: 200 g of all-purpose flour is ≈ 1 ⅝ cups (1.6).
- Grams: to the nearest gram; to 0.1 g below 10 g. Table fractions (¾, ½, ⅓, ¼ cup) are calculated from the 1-cup weight and rounded separately, so four ¼-cup values can add up to a gram more or less than 1 cup.
- Tablespoons: US tablespoons of 14.787 ml (1/16 of a US cup), to one decimal place in the cup calculator.
- Millilitres: to the nearest whole millilitre.
Calculations always use the unrounded values; rounding happens only when a number is displayed.
Corrections
If a weight doesn't match your ingredient, tell us the brand, the cup size and how you filled it. We change the data file only when a published source supports the change.