SAE (imperial) tools are sized in fractions of an inch, metric tools in millimetres. Some pairs are near-identical, such as 19 mm and 3/4″ (19.05 mm); others, like 13 mm and 1/2″ (12.7 mm), are too far apart and will round off a bolt head.
How to use the Metric to SAE Calculator
- Metric size
- Every result field is editable: type into Decimal inches and Metric size plus every other field update to match.
Results update as you type, and every field accepts the units shown in its menu.
How it works
Millimetres are divided by 25.4. The result is rounded to the nearest 1/64″ and 1/16″, and the difference is reported in millimetres.
Metric and SAE wrench equivalents
| mm | Decimal in | Nearest SAE | Difference |
|---|---|---|---|
| 6 | 0.2362 | 0.25″ | +0.35 mm |
| 8 | 0.3150 | 0.3125″ | -0.06 mm |
| 10 | 0.3937 | 0.375″ | -0.48 mm |
| 11 | 0.4331 | 0.4375″ | +0.11 mm |
| 12 | 0.4724 | 0.5″ | +0.70 mm |
| 13 | 0.5118 | 0.5″ | -0.30 mm |
| 14 | 0.5512 | 0.5625″ | +0.29 mm |
| 15 | 0.5906 | 0.5625″ | -0.71 mm |
| 16 | 0.6299 | 0.625″ | -0.12 mm |
| 17 | 0.6693 | 0.6875″ | +0.46 mm |
| 19 | 0.7480 | 0.75″ | +0.05 mm |
| 22 | 0.8661 | 0.875″ | +0.22 mm |
| 24 | 0.9449 | 0.9375″ | -0.19 mm |
| 27 | 1.0630 | 1.0625″ | -0.01 mm |
| 30 | 1.1811 | 1.1875″ | +0.16 mm |
| 32 | 1.2598 | 1.25″ | -0.25 mm |
What each result means
- Decimal inches = [Metric size] ÷ 25.4
- Nearest 1/64″ = round([Metric size] ÷ 25.4 × 64) ÷ 64
- Nearest 1/16″ (common wrench sizes) = round([Metric size] ÷ 25.4 × 16) ÷ 16
- Difference from 1/16″ size = (round([Metric size] ÷ 25.4 × 16) ÷ 16) × 25.4 – [Metric size]
Formula
inches = mm ÷ 25.4; nearest SAE size = round(inches × 64) ÷ 64Worked example
Inputs — Metric size: 19 mm.
Results — Decimal inches = 0.748 in; Nearest 1/64″ = 3/4; Nearest 1/16″ (common wrench sizes) = 3/4; Difference from 1/16″ size = 0.05 mm.
Frequently asked questions
Is 19 mm the same as 3/4″?
Nearly: 3/4″ is 19.05 mm, a 0.05 mm difference.
Can I use a 13 mm socket on a 1/2″ bolt?
It will be loose by 0.3 mm and may round the bolt; use the correct tool.
What formula does the Metric to SAE Calculator use?
inches = mm ÷ 25.4; nearest SAE size = round(inches × 64) ÷ 64.