Metric to SAE Calculator

Created by Davide Borchia
Reviewed by Anna Szczepanek, PhD
Last updated: Jan 18, 2023

Our metric to SAE calculator will be a fundamental tool in your arsenal: you will learn how to quickly convert between metric to SAE, a critical knowledge in any workshop and engineering environment. Has it ever happened to you to start tightening a bolt just to find out that your wrench was not fitting perfectly? If yes, you were probably trying to use a metric wrench with an SAE bolt or vice-versa. Keep reading our article to learn:

  • What is the SAE system of measurement;
  • How to calculate the conversion from metric to SAE units;
  • The metric to SAE chart for inches and millimeters.

What is the SAE system?

The SAE system of measurement units is a collection of measurement units, a subsystem of the imperial system used by American engineers, mechanics, and hobbyists: SAE stands for society of automotive engineers.

SAE units are widely used to measure machines, mechanical components, screws, and bolts. A measurement in SAE units corresponds to a measurement in inches (most often) or feet but is almost always expressed as fraction: in the following sections we will teach you how to calculate the conversion from metric to SAE, and we will show you the metric to SAE chart for a quick, at-a-glance conversion of bolt sizes and much more!

Calculate the conversion from metric to SAE

To convert from metric to SAE, you only need to learn a simple conversion between metric and imperial units. In most situations, you will have to convert millimeters to inches since these are the units most commonly used:

1 mm=0.03937 in1\ \mathrm{mm} = 0.03937\ \mathrm{in}

You can calculate the metric to SAE conversion between other units by using the following rules:

1 in=112 ft=11213 yd1\ \mathrm{in} = \frac{1}{12}\ \mathrm{ft} = \frac{1}{12}\cdot\frac{1}{3}\ \mathrm{yd}

The story is different (and easier) within the metric system:

1 mm=110 cm=11000 m1\ \mathrm{mm} = \frac{1}{10}\ \mathrm{cm} = \frac{1}{1000}\ \mathrm{m}

However, the result of this conversion is not exactly what we need in most situations! Bolt, nut, and screw sizes come in standardized sizes: 3/4"3/4", 3/8"3/8", and 8 mm8\ \mathrm{mm}, and so on; to understand quickly which wrench to use you may have more luck using a metric to SAE chart.

The metric to SAE chart

Our calculator for the metric to SAE conversion gives you the result you deserve but not the result you need. In your toolbox, you will find wrenches and keys of slightly different sizes, often marked with neat ratios like 3/43/4 and 15/1615/16. Using a metric to SAE chart, you can quickly find the best fitting SAE wrench for a metric bolt, and vice-versa. Here is it:

Metric to SAE chart

Other metric and imperial converters

Discover more conversion between and within the imperial and metric systems with our suite of dedicated tools:


Can I use a metric wrench on a SAE bolt?

Yes! In most cases, you can use a metric wrench on an SAE bolt and vice-versa: the difference in size is often minimal. However, be careful: slightly larger wrenches can deform, wear, and even strip a bolt. It's always better to use the right key!

How do I convert from metric to SAE?

To calculate the conversion from metric to SAE, follow these easy steps:

  1. Measure the size of the bolt in millimeters.
  2. Multiply the size in millimeters by 0.03937 to find the size in inches.
  3. Find a ratio with a result similar to the conversion you performed. The most used denominators are powers of 2.
  4. You can also use a conversion chart between metric and SAE: you will save some time!

What is 19 mm in SAE?

19 mm equals 0.748 in. However, you will not find such a tool in your toolbox. The correct wrench size is 3/4 in: this tool would be slightly larger than what you need, but it would not matter much!

What are the most common conversions form metric to SAE?

In the next list you can find the most common conversions between metric and SAE:

  • 24 mm = 15/16 in
  • 22 mm = 7/8 in
  • 21 mm = 13/16 in
  • 19 mm = 3/4 in
  • 16 mm = 5/8 in
  • 14 mm = 9/16 in
  • 13 mm = 1/2 in
  • 11 mm = 7/16 in
  • 10 mm = 3/8 in
  • 8 mm = 5/16 in
Davide Borchia
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