How to Convert Your Metric Wrench Set to Imperial Units

Several wrenches and screws in a pile against a white background.

While many people have both a metric wrench set and an imperial, or standard, set, if you only have a metric set available, no need to worry. It doesn’t matter if you find yourself confronted with directions using imperial measurements or you come across a bolt that none of your metric wrenches seem to fit, you do not need to go and buy an entirely new set of wrenches. It is a relatively simple mathematical procedure to convert the metric units of measurement to the imperial standard so you can pick the right tool for the job.

The Formula

Until the world converts to one standard of measurement or the other, you can use this formula to determine the imperial size you will need from a metric measurement. Multiply the metric amount by 0.39216 to convert centimeters to inches. Also, if you need to convert meters to feet, multiply the meters by 3.33333, and the resulting amount will be in feet.

The Chart

Rather than going through the trouble of finding your calculator, you can reference the chart below for easy conversions.

1 mm - n/a
2 mm - n/a
3 mm - 1/8 inches
4 mm - 5/32 inches
5 mm - 3/16 inches
6 mm - 1/4 inches
7 mm - 9/32 inches
8 mm - 5/16 inches
9 mm - 11/32 inches
10 mm - 13/32 inches
11 mm - 7/16 inches
12 mm - 15/32 inches
13 mm - 1/2 inches
14 mm - 9/16 inches
15 mm - 19/32 inches
16 mm - 5/8 inches
17 mm - 21/32 (11/16) inches
18 mm - 23/32 inches
19 mm - 3/4 inches
20 mm - 25/32 inches
21 mm - 27/32 inches
22 mm - 7/8 inches
23 mm - 29/32 inches
24 mm - 15/16 inches
25 mm - 1 inches

This chart is interchangeable in that it goes both ways, so it is useful if you need to convert metric units to imperial units, or vice versa. One millimeter and two millimeter both have "n/a" next to them because neither of those units have a counterpart in the imperial system.

When to Use

Obviously, you would use the conversion chart or the formula when you need to convert the measurements of your metric wrench set into imperial measurements. One instance in particular where you might find yourself needing to convert units is if you need to work on an American car. Cars made in America primarily use the imperial standard of measurements for various components, and as such, can be difficult to work on if you only have a metric wrench set. Similarly, various appliances made in the United States, such as washers and dryers, lawn mowers and other equipment that use small motors, and many other things all use the imperial standard of measurements.

If you find yourself frequently working on equipment and appliances that make use of the imperial standard of measurements, it may be a good idea for you to copy this list of conversations, as well as the formula, and place it in a convenient location. It will save you time in the long run.