SHOP REFERENCE / CONVERSION

Metric to SAE Socket Conversion

Compare the exact measurement with the nearest nominal socket opening. A close number does not prove that a different socket will grip a fastener safely.

Open the Socket Finder tool

EXACT CONVERSION1 IN. = 25.4 MM

The arithmetic is exact. The socket matches in the charts are approximate unless their openings are identical.

CONVERSION / 01

Metric → SAE

Converted inch value, nearest listed SAE opening, and the nominal difference.

Metric socket opening to inches and nearest listed SAE socket opening
Metric	Converted (4 decimals)	Closest SAE*	Difference
4 mm	0.1575 in.	5/32 in.	0.031 mm
4.5 mm	0.1772 in.	3/16 in.	0.262 mm
5 mm	0.1969 in.	3/16 in.	0.238 mm
5.5 mm	0.2165 in.	7/32 in.	0.056 mm
6 mm	0.2362 in.	1/4 in.	0.350 mm
7 mm	0.2756 in.	9/32 in.	0.144 mm
8 mm	0.3150 in.	5/16 in.	0.062 mm
9 mm	0.3543 in.	11/32 in.	0.269 mm
10 mm	0.3937 in.	3/8 in.	0.475 mm
11 mm	0.4331 in.	7/16 in.	0.112 mm
12 mm	0.4724 in.	1/2 in.	0.700 mm
13 mm	0.5118 in.	1/2 in.	0.300 mm
14 mm	0.5512 in.	9/16 in.	0.288 mm
15 mm	0.5906 in.	9/16 in.	0.712 mm
16 mm	0.6299 in.	5/8 in.	0.125 mm
17 mm	0.6693 in.	11/16 in.	0.462 mm
18 mm	0.7087 in.	11/16 in.	0.538 mm
19 mm	0.7480 in.	3/4 in.	0.050 mm
20 mm	0.7874 in.	13/16 in.	0.638 mm
21 mm	0.8268 in.	13/16 in.	0.362 mm
22 mm	0.8661 in.	7/8 in.	0.225 mm
23 mm	0.9055 in.	7/8 in.	0.775 mm
24 mm	0.9449 in.	15/16 in.	0.188 mm
25 mm	0.9843 in.	1 in.	0.400 mm
26 mm	1.0236 in.	1 in.	0.600 mm
27 mm	1.0630 in.	1-1/16 in.	0.012 mm
28 mm	1.1024 in.	1-1/8 in.	0.575 mm
29 mm	1.1417 in.	1-1/8 in.	0.425 mm
30 mm	1.1811 in.	1-3/16 in.	0.162 mm
31 mm	1.2205 in.	1-1/4 in.	0.750 mm
32 mm	1.2598 in.	1-1/4 in.	0.250 mm

CONVERSION / 02

SAE → Metric

Converted millimeter value, nearest listed metric opening, and the nominal difference.

SAE socket opening to millimeters and nearest listed metric socket opening
SAE	Converted (4 decimals)	Closest metric*	Difference
5/32 in.	3.9688 mm	4 mm	0.031 mm
3/16 in.	4.7625 mm	5 mm	0.238 mm
7/32 in.	5.5562 mm	5.5 mm	0.056 mm
1/4 in.	6.3500 mm	6 mm	0.350 mm
9/32 in.	7.1438 mm	7 mm	0.144 mm
5/16 in.	7.9375 mm	8 mm	0.062 mm
11/32 in.	8.7312 mm	9 mm	0.269 mm
3/8 in.	9.5250 mm	10 mm	0.475 mm
7/16 in.	11.1125 mm	11 mm	0.112 mm
1/2 in.	12.7000 mm	13 mm	0.300 mm
9/16 in.	14.2875 mm	14 mm	0.288 mm
5/8 in.	15.8750 mm	16 mm	0.125 mm
11/16 in.	17.4625 mm	17 mm	0.462 mm
3/4 in.	19.0500 mm	19 mm	0.050 mm
13/16 in.	20.6375 mm	21 mm	0.362 mm
7/8 in.	22.2250 mm	22 mm	0.225 mm
15/16 in.	23.8125 mm	24 mm	0.188 mm
1 in.	25.4000 mm	25 mm	0.400 mm
1-1/16 in.	26.9875 mm	27 mm	0.012 mm
1-1/8 in.	28.5750 mm	29 mm	0.425 mm
1-3/16 in.	30.1625 mm	30 mm	0.162 mm
1-1/4 in.	31.7500 mm	32 mm	0.250 mm

*“Closest” means smallest numerical difference among the nominal socket sizes listed here. Every cross-system pairing in these tables is approximate; the values do not account for manufacturing tolerances or guarantee usable fit. Converted values are rounded to four decimal places; differences are shown in millimeters and rounded to 0.001 mm.

AT THE BENCH

Common size examples

19 mm ↔ 3/4 in.

3/4 in. is exactly 19.05 mm, just 0.05 mm larger than 19 mm. The numbers are close, but check the actual socket on the head.

13 mm ↔ 1/2 in.

1/2 in. is exactly 12.7 mm, 0.3 mm smaller than 13 mm. Do not force the smaller socket onto a 13 mm head.

10 mm ↔ 3/8 in.

3/8 in. is exactly 9.525 mm, 0.475 mm smaller than 10 mm. This is the nearest size in the listed SAE range, but a 10 mm socket is the correct first choice.

The size marked on a socket describes the nominal opening across the fastener’s flats. It does not describe the bolt thread diameter or the square ratchet drive size.

Enter a size in the live Socket Finder converter →

Reference and method

Calculations use the exact inch definition from NIST: 1 in. = 25.4 mm. The metric size range (4–32 mm) and SAE fractions (5/32–1-1/4 in.) are listed in socket catalogs such as TEKTON’s small socket sets, metric 1/2 in. drive sets and SAE 1/2 in. drive sets. The nearest opening and difference are calculated from those nominal sizes. Some sets skip sizes or include others.