How we calculate
Units we use
| Constant | Value | Source |
|---|---|---|
| US customary cup | 236.5882365 mL | NIST Handbook 44 Appendix C |
| US tablespoon | 1/16 cup = 14.78676478 mL | NIST Handbook 44 |
| US teaspoon | 1/48 cup = 4.928921594 mL | NIST Handbook 44 |
| US legal cup (nutrition labels) | 240 mL | FDA, 21 CFR 101.9(b)(5)(viii) |
| US fluid ounce | 29.5735295625 mL | NIST Handbook 44 |
| Avoirdupois ounce | 28.349523125 g | NIST Handbook 44 |
| 1 stick of US butter | 1/2 cup = 8 tbsp = 4 oz = 113.4 g | US butter wrapper convention; 4 oz x 28.3495 g |
| Large egg, without shell | 50 g | USDA FoodData Central SR Legacy, "Egg, whole, raw, fresh", 1 large |
Ingredient weights
USDA values come from the FoodData Central SR Legacy release, using each food's household portion for 1 cup. King Arthur values come from their published ingredient weight chart; where they list 1/2 cup or 1/4 cup, we multiplied up to a full cup. Tablespoon and teaspoon figures are the cup weight divided by 16 and 48. The full table is on the ingredient weights page.
Rounding
Grams are shown to 1 decimal below 100 g and as whole grams above. Cup and spoon results are rebuilt into standard US measures, down to 1/8 teaspoon. When a result falls between spoon sizes we say "about".
What we compare
Each converter can switch between USDA and King Arthur figures. We flag differences over 3%.
Checks
Every converter has automated tests for its worked examples, tables and FAQ numbers. We also compare results with King Arthur's published chart before each update.
Sources
- USDA FoodData Central SR Legacy · accessed 2026-10-14
- King Arthur Baking Ingredient Weight Chart · accessed 2026-10-14
- NIST Handbook 44 Appendix C · accessed 2026-10-14