🔧 Automotive Tools Converter
SAE vs Metric wrench sizes, torque conversion (ft-lb ↔ Nm), and drill bit sizes (inches ↔ mm). Everything a mechanic needs — with full reference tables.
SAE ↔ Metric Wrench Converter
Complete SAE ↔ Metric Reference Table
⚠️ SAE and metric sizes are not exactly interchangeable — always use the correct size to avoid rounding off fasteners. The table shows the closest match, not an exact fit.
| SAE Size | Decimal (in) | Exact (mm) | Closest Metric |
|---|---|---|---|
| 1/4" | 0.2500" | 6.35 mm | 6 mm |
| 9/32" | 0.2810" | 7.14 mm | 7 mm |
| 5/16" | 0.3125" | 7.94 mm | 8 mm |
| 11/32" | 0.3440" | 8.74 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 Don't Match Perfectly
SAE (Society of Automotive Engineers) sizes use fractions of an inch. Metric sizes use whole millimeters. Since 1 inch = 25.4 mm exactly, most SAE fractions land between metric sizes. For example, 3/8" = 9.525 mm — between 9 mm and 10 mm.
Using the wrong size risks rounding off the bolt head corners. In a pinch, a metric wrench 0.2–0.5 mm larger than the SAE size will usually fit without damage, but always use the correct size for critical fasteners.
SAE vs Metric: Why American Mechanics Need Both
American-made vehicles from Ford, GM, and Chrysler have historically used SAE fasteners — but since the 1980s, even domestic cars use a mix of both systems. Import vehicles (Toyota, Honda, BMW, Mercedes, Audi, VW) are almost entirely metric. Any mechanic working on a variety of vehicles needs both SAE and metric tool sets.
The frustration comes when you are mid-job and reach for the closest size. A 3/8" socket (9.525 mm) and a 10 mm socket are just 0.5 mm apart — close enough to fit on some fasteners, but loose enough to round off the corners on others. Using the closest available size in a pinch is fine for low-torque fasteners; for cylinder heads, wheel studs, and brake calipers, always use the correct size.
Torque specs are the other major cross-system headache. A Haynes or Chilton manual for an American car gives torque in ft-lb. A factory service manual for a European or Japanese car gives Nm. Most quality torque wrenches have both scales, but if yours only has one, this converter gives you the exact equivalent in seconds.