SAE to metric conversion chart

Russell Bateman
November 2025
last update:

You have a 13 mm bolt, but no 13 mm wrench in your kit. Can you use a ½" wrench instead? Maybe, but tolerances matter. Even a small mismatch can cause rounding or slipping, especially if the bolt is rusted or torqued tightly. Here's a list of close comparisons:

SAE¹ to Metric Wrench Conversion Chart

SAE (inches)	Metric	Notes
5/32	4 mm	Slightly loose fit
3/16	4.5 mm	Rare metric size
7/32	5.5 mm	Not an exact match
¼	6 mm	Very close
5/16	8 mm	Near match
11/32	9 mm	Slightly tight fit
⅜	10 mm	Very close
7/16	11 mm	Not quite the same
½	13 mm	Often interchangeable
9/16	14 mm	Close, but slightly tight
⅝	16 mm	Fair match
11/16	17 mm	Very close
¾	19 mm	Often used interchangeably
13/16	21 mm	Some overlap
⅞	22 mm	Close fit
15/16	24 mm
1	25.4 mm	Exact conversion

1⅛	29 mm	Common in heavy machinery and plumbing
1¼	32 mm	Often used for industrial applications
1⅜	35 mm	Useful in large automotive bolts
1½	38 mm	Close match for structural hardware
1⅝	41 mm	Slightly oversized; check fit closely
1¾	45 mm	Used in HVAC and construction work
1⅞	48 mm	Close enough for most high-torque jobs
2	51 mm	Exact match for large bolt heads

Notes

¹ Society of American Engineers.

Common sizes in use...

The cells next to each other, unlike the first chart, are not meant as equivalents. These are just lists of common SAE and common metric gauges in use for the tasks listed.

...automotive

SAE	metric
⅜	8 mm
7/16	10 mm
½	13 mm
9/16	14 mm
	15 mm
	17 mm
	19 mm

...plumbing

These are common screw head and nut sizes—not pipe or hose gauges.