Wrench & Socket Size Converter

Find the closest metric or SAE wrench or socket size, and whether it is a safe substitute.

How to use the Wrench & Socket Size Converter

Choose SAE or metric.
Enter the size (e.g. 1/2 or 13).
Read the closest equivalent and the difference.

How it works

Wrench sizes refer to the distance across the flats of the bolt head. SAE sizes are in fractions of an inch; metric sizes are whole millimeters. Some pairs are almost identical — 3/4″ (19.05 mm) and 19 mm — while others differ by enough to round off a nut. A difference of about 0.2 mm or less is generally a usable fit.

Close SAE / metric pairs

SAE	mm	Metric	Fit
1/4″	6.35	6 mm	Loose
5/16″	7.94	8 mm	Good
3/8″	9.53	10 mm	Loose
7/16″	11.11	11 mm	Good
1/2″	12.70	13 mm	Loose
9/16″	14.29	14 mm	Loose
5/8″	15.88	16 mm	Good
3/4″	19.05	19 mm	Very good

Frequently asked questions

What is 1/2 inch in mm wrench?

12.7 mm — 13 mm is the closest metric size.

What size is a 10 mm socket in SAE?

About 3/8″ (9.53 mm) — slightly smaller, not a good fit.

Is 19 mm the same as 3/4″?

Nearly — 3/4″ is 19.05 mm.

Can I use SAE wrenches on metric bolts?

Only where the sizes are very close; otherwise you risk rounding the bolt.