Metric to SAE Wrench Size Converter

What Is SAE?

SAE stands for Society of Automotive Engineers. In workshops and garages, SAE refers to imperial wrench and bolt sizes, usually expressed as fractional inches like 3/8" or 7/16". Metric fasteners use millimeters. Mixing the two is common, so a quick conversion chart saves time.

Metric to SAE Conversion

The base conversion between millimeters and inches is:

$$1\ \text{in} = 25.4\ \text{mm}$$

$$mm = in \times 25.4$$

In practice, you rarely find a wrench at the exact decimal inch. Use the nearest standard SAE size instead.

Common Wrench Size Equivalents

8 mm ≈ 5/16 in
10 mm ≈ 3/8 in
13 mm ≈ 1/2 in
16 mm ≈ 5/8 in
19 mm ≈ 3/4 in
24 mm ≈ 15/16 in

Frequently Asked Questions

Can I use a metric wrench on an SAE bolt?

Often yes, if the sizes are close. A 19 mm wrench fits a 3/4 inch bolt well. Slightly oversized wrenches can round bolt heads, so use the closest standard size.

What SAE wrench fits a 19 mm bolt?

A 3/4 inch wrench is the standard equivalent for 19 mm. The exact decimal conversion is 0.748 inches, but 3/4 inch is the tool you will find in a toolbox.

How do I convert mm to fractional inches?

Divide millimeters by 25.4 to get decimal inches, then match to the nearest common fraction such as 1/2, 9/16, or 3/4.

Why are SAE sizes in fractions?

Imperial fasteners and tools evolved using binary fractions (halves, quarters, eighths, sixteenths). That is why wrench labels show values like 7/16 instead of decimals.

Is 24 mm the same as 15/16 inch?

Close enough for most workshop use. 24 mm equals 0.9449 inches, and 15/16 inch equals 0.9375 inches. Mechanics commonly treat them as interchangeable.

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Metric to SAE Calculator

What Is SAE?

Metric to SAE Conversion

Common Wrench Size Equivalents

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Frequently Asked Questions

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