Sources and Methodology
Measurement charts are only useful if they're right. This page explains where each set of numbers comes from and how we check them.
Sources by topic
| Topic | Source |
|---|---|
| Unit definitions (length, mass, volume) | NIST Handbook 44, Appendix C and NIST SP 811 |
| Ingredient weights per cup | USDA FoodData Central (SR Legacy household measures) |
| Wire gauge (AWG) | ASTM B258 for diameters; NFPA 70 (National Electrical Code) Table 310.16 for ampacity |
| Sheet metal gauge | Manufacturers' Standard Gauge for sheet steel; ASTM A568 for tolerances |
| Wind force | WMO and NOAA National Weather Service Beaufort scale |
| Yarn weights | Craft Yarn Council Standard Yarn Weight System |
| Shoe sizes | UK barleycorn and EU Paris point definitions; ISO 9407 (Mondopoint) |
How values are calculated and rounded
- Exact definitions (for example 1 inch = 2.54 cm) are used at full precision; only the displayed result is rounded.
- Where a standard defines a formula (AWG diameters, EU shoe sizes), we compute from the formula rather than copying a table, then round for display.
- Kitchen measures are rounded to the nearest combination of a cup fraction (1/4, 1/3, 1/2, 2/3, 3/4) and up to 3 tablespoons, and the exact decimal is always shown too.
- Numbers are rounded half away from zero, the same way in the converters and the printed tables.
How we test
Each converter and the table on its page are built from one data file. Before any update is published, an automated test runs every converter in a real browser with normal, reference, invalid and boundary inputs, and checks that its answers match the published table and the source values. If any test fails, the update doesn't go live.
Corrections log
No corrections yet. The site relaunched on November 5, 2026. If you spot an error, please contact us with the page and the value; we'll fix it and note the change here.