While the United States still relies heavily on the imperial system of measurement, which measures mass in pounds and ounces and height in feet and inches, most other countries use the metric system, which measures mass in kilograms and grams and height in meters and centimeters. If you have a measurement in inches and want to convert it to millimeters, the calculation is quick and simple. Use a calculator to make it even quicker and avoid mathematical errors.
Convert a Fraction to a Decimal
If you have a measurement of 7/8 inches, convert it to a decimal. Simply work out 7 ÷ 8 = 0.875. Use 0.875 for the rest of your calculation.
Understand the Relationship Between Inches and Millimeters
One inch is the same as 25.4 millimeters. So to convert your value in inches to millimeters, multiply it by 25.4. In this case, work out 0.875 x 25.4 = 22.225. This means 7/8 inches is the same as 22.225 millimeters.
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Check Your Answer
Use an online conversion tool to check your answer. Some of these have drop-down boxes to let you change your units. Select inches and millimeters. Input 0.875 into the inches field and make sure the value in the millimeters field is 22.225.