🔧 Automotive tools converter
SAE and metric wrench sizes, torque in ft-lb and Nm, and drill bit sizes in inches and millimeters, with full reference tables.
SAE ↔ metric wrench converter
SAE to metric reference table
SAE and metric sizes are not interchangeable. The closest metric size is listed for reference; always use the correct size on critical fasteners to avoid rounding the bolt head.
| SAE size | Decimal (in) | Exact (mm) | Closest metric |
|---|---|---|---|
| 1/4" | 0.2500" | 6.35 mm | 6 mm |
| 9/32" | 0.2813" | 7.14 mm | 7 mm |
| 5/16" | 0.3125" | 7.94 mm | 8 mm |
| 11/32" | 0.3438" | 8.73 mm | 9 mm |
| 3/8" | 0.3750" | 9.52 mm | 10 mm |
| 7/16" | 0.4375" | 11.11 mm | 11 mm |
| 1/2" | 0.5000" | 12.70 mm | 13 mm |
| 9/16" | 0.5625" | 14.29 mm | 14 mm |
| 5/8" | 0.6250" | 15.88 mm | 16 mm |
| 11/16" | 0.6875" | 17.46 mm | 17 mm |
| 3/4" | 0.7500" | 19.05 mm | 19 mm |
| 13/16" | 0.8125" | 20.64 mm | 21 mm |
| 7/8" | 0.8750" | 22.22 mm | 22 mm |
| 15/16" | 0.9375" | 23.81 mm | 24 mm |
| 1" | 1.0000" | 25.40 mm | 25 mm |
| 1-1/16" | 1.0625" | 26.99 mm | 27 mm |
| 1-1/8" | 1.1250" | 28.57 mm | 29 mm |
| 1-1/4" | 1.2500" | 31.75 mm | 32 mm |
| 1-3/8" | 1.3750" | 34.92 mm | 35 mm |
| 1-1/2" | 1.5000" | 38.10 mm | 38 mm |
Why SAE and metric sizes don't match
SAE sizes are fractions of an inch, metric sizes are whole millimeters, and 1 inch is exactly 25.4 mm. Most fractions land between two metric sizes: 3/8" is 9.525 mm, between 9 mm and 10 mm. Only a few pairs are close enough to swap in a pinch, such as 3/4" and 19 mm (19.05 mm).
Why American mechanics need both systems
Older American vehicles used SAE fasteners, but most cars built since the 1980s mix both systems, and imports from Japan, Korea and Europe are almost entirely metric. A mechanic working on a variety of vehicles needs both socket sets.
Close sizes are tempting mid-job. A 3/8" socket (9.525 mm) and a 10 mm socket differ by about half a millimeter, enough to round off a tight bolt. For cylinder heads, wheel studs and brakes, use the exact size and torque specification.
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