How do I convert metric wrench sizes to SAE?

Convert the metric size from millimeters to inches by dividing by 25.4, then compare it with common SAE fractional sizes. This converter finds the closest practical match and shows the size difference.

Is 13 mm the same as 1/2 inch?

No. A 1/2 inch wrench is 12.7 mm. A 13 mm wrench is about 0.3 mm larger, so it is close but not identical.

Can I use the closest SAE socket on a metric bolt?

Sometimes for light work, but exact fit is best. A loose or undersized substitute can round fasteners, especially on tight, rusty, or high-torque bolts.

Garage & workshop converter

Wrench Size Converter

Convert metric wrench and socket sizes to the closest SAE inch size, or convert SAE fractions to millimeters. Get the nearest match, the exact difference, and a plain-English fit note before you grab the wrong socket.

Convert a wrench or socket size

Enter a metric size like 13 mm or an SAE size like 1/2. Results update instantly.

Starting unit Wrench or socket size Use case

Closest match 13 mm ≈ 1/2 in

1/2 inch is 0.300 mm smaller than 13 mm.

Exact decimal 0.5118 in

Difference 0.300 mm

13 mm is close to 1/2 inch, but the sizes are not identical.

Metric to SAE wrench conversion basics

Metric wrench sizes are measured in millimeters across the flats of the fastener. SAE wrench sizes are measured in inch fractions. The math is simple: 1 inch = 25.4 mm, but real tool fit depends on how close the nearest standard size is.

10 mm is closest to 3/8 inch, but 3/8 inch is smaller.
13 mm is close to 1/2 inch, but 13 mm is slightly larger.
19 mm is very close to 3/4 inch.

When the closest size is good enough

A close substitute may work for loose fasteners or quick checks. For tight, corroded, shallow, or high-torque fasteners, use the exact metric or SAE size whenever possible. A loose socket can round a nut faster than a raccoon in a snack drawer.

The fit note below the result calls out whether the nearest match is larger or smaller so you can choose carefully.

Metric to SAE wrench size chart

Metric size	Closest SAE	SAE in mm	Difference

SAE to metric socket size chart

SAE size	Exact mm	Closest metric	Difference

Wrench size conversion FAQ

What SAE size is closest to 13 mm?

1/2 inch is closest. It equals 12.7 mm, which is 0.3 mm smaller than 13 mm.

What metric size is closest to 3/4 inch?

19 mm is the closest common metric wrench size. 3/4 inch equals 19.05 mm.

Are socket sizes and wrench sizes converted the same way?

Yes. Both refer to the size across the flats of the fastener. The fit can still vary by tool quality, fastener wear, rust, and whether you are using a six-point or twelve-point socket.