Socket Size Chart
Every common SAE socket with its exact metric equivalent, the nearest stocked metric size and whether the swap is safe.
Quick answer
Multiply inches by 25.4 for the exact metric size. The genuinely interchangeable pairs are 3/4" ↔ 19 mm, 3/8" ↔ 10 mm, 5/16" ↔ 8 mm and 1/4" ↔ 6 mm. Common near-misses: 1/2" is 12.70 mm against a 13 mm socket, and 9/16" is 14.29 mm against 14 mm.
SAE to metric socket conversion
Difference is the gap between the SAE size and the nearest stocked metric socket.
| SAE | Decimal (in) | Exact (mm) | Nearest metric | Difference (mm) | Substitution |
|---|---|---|---|---|---|
| 5/32" | 0.1563 | 3.97 | 4 mm | 0.03 | Interchangeable |
| 3/16" | 0.1875 | 4.76 | 5 mm | 0.24 | Usable, slight slop |
| 7/32" | 0.2188 | 5.56 | 5.5 mm | 0.06 | Interchangeable |
| 1/4" | 0.2500 | 6.35 | 6 mm | 0.35 | Do not substitute |
| 9/32" | 0.2813 | 7.14 | 7 mm | 0.14 | Usable, slight slop |
| 5/16" | 0.3125 | 7.94 | 8 mm | 0.06 | Interchangeable |
| 11/32" | 0.3438 | 8.73 | 9 mm | 0.27 | Usable, slight slop |
| 3/8" | 0.3750 | 9.52 | 10 mm | 0.47 | Do not substitute |
| 7/16" | 0.4375 | 11.11 | 11 mm | 0.11 | Interchangeable |
| 1/2" | 0.5000 | 12.70 | 13 mm | 0.30 | Usable, slight slop |
| 9/16" | 0.5625 | 14.29 | 14 mm | 0.29 | Usable, slight slop |
| 19/32" | 0.5938 | 15.08 | 15 mm | 0.08 | Interchangeable |
| 5/8" | 0.6250 | 15.88 | 16 mm | 0.12 | Usable, slight slop |
| 11/16" | 0.6875 | 17.46 | 17 mm | 0.46 | Do not substitute |
| 3/4" | 0.7500 | 19.05 | 19 mm | 0.05 | Interchangeable |
| 13/16" | 0.8125 | 20.64 | 21 mm | 0.36 | Do not substitute |
| 7/8" | 0.8750 | 22.23 | 22 mm | 0.23 | Usable, slight slop |
| 15/16" | 0.9375 | 23.81 | 24 mm | 0.19 | Usable, slight slop |
| 1" | 1.0000 | 25.40 | 25 mm | 0.40 | Do not substitute |
| 1-1/16" | 1.0625 | 26.99 | 27 mm | 0.01 | Interchangeable |
| 1-1/8" | 1.1250 | 28.58 | 29 mm | 0.42 | Do not substitute |
| 1-1/4" | 1.2500 | 31.75 | 32 mm | 0.25 | Usable, slight slop |
| 1-5/16" | 1.3125 | 33.34 | 33 mm | 0.34 | Do not substitute |
| 1-3/8" | 1.3750 | 34.92 | 35 mm | 0.08 | Interchangeable |
| 1-1/2" | 1.5000 | 38.10 | 38 mm | 0.10 | Interchangeable |
Published standard — source: Exact fraction-to-millimetre conversion at 25.4 mm per inch
Source & method: Substitution guidance uses a 0.12 mm interchangeable threshold and 0.30 mm usable-with-care threshold, based on typical hex fastener tolerances.
Safe swaps at a glance
| Pair | Difference (mm) | Verdict |
|---|---|---|
| 5/32" ↔ 4 mm | 0.03 | Interchangeable |
| 7/32" ↔ 5.5 mm | 0.06 | Interchangeable |
| 5/16" ↔ 8 mm | 0.06 | Interchangeable |
| 7/16" ↔ 11 mm | 0.11 | Interchangeable |
| 19/32" ↔ 15 mm | 0.08 | Interchangeable |
| 3/4" ↔ 19 mm | 0.05 | Interchangeable |
| 1-1/16" ↔ 27 mm | 0.01 | Interchangeable |
| 1-3/8" ↔ 35 mm | 0.08 | Interchangeable |
| 1-1/2" ↔ 38 mm | 0.10 | Interchangeable |
Frequently asked
- What metric socket replaces 1/2 inch?
- A 13 mm socket is the closest metric size to 1/2 inch. 1/2 inch is 12.70 mm, so a 13 mm socket is 0.30 mm loose — usable in a pinch on a well-shaped fastener, but not ideal on a tight or rounded nut.
- Which SAE and metric sockets are practically interchangeable?
- 3/8 inch and 10 mm differ by 0.13 mm, 5/16 inch and 8 mm by 0.14 mm, and 3/4 inch and 19 mm by 0.05 mm. Those are the safest swaps. Anything over about 0.25 mm of slop risks rounding the fastener.
- How do I convert socket sizes from inches to millimetres?
- Multiply the decimal inch size by 25.4. A 9/16 inch socket is 0.5625 × 25.4 = 14.29 mm, which is why a 14 mm socket is the closest metric equivalent.
- Should I use an SAE socket on a metric bolt?
- Only when the difference is under about 0.15 mm and the fastener is in good condition. Using an oversized socket is the most common cause of rounded bolt heads.
- What socket sizes do electricians use most?
- 7/16, 1/2 and 9/16 inch cover most strut, panel and enclosure hardware, with 3/8 inch for smaller machine screws and 3/4 inch and up for lug and busbar hardware.
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