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How to convert screw sizes

Updated April 17, 2017

Screw sizes are measured using both the metric and imperial measurement types. The metric form of measurements gives the screw's gauge (diameter) and the screw's length in millimetres. The imperial method, however, uses inches to measure the screws length and a unit of measurement entirely unique to screws to measure the gauge. With a few simple measurement conversion equations, you can convert between these two forms of measurement to ensure you are using the proper screws for your project.

Insert the length of the screw in millimetres into the calculator.

Multiply the number by 0.03937 to determine the length of the screw in inches.

Insert the gauge of the screw in millimetres into the calculator.

Multiply the number by 0.03937 to determine the gauge of the screw in inches.

Subtract 0.06 from the gauge of the screw in inches.

Divide the new number by 0.013. The result is the imperial measurement of the screw's gauge.

Write the screw size in the following format: (imperial screw gauge size) x (screw length in inches).

Insert the length of the screw in inches into the calculator. Remember that the imperial screw measurement format is (gauge of screw) x (length of screw).

Multiply the number by 25.4 to convert the inches to millimetres.

Insert the screw's gauge number into the calculator.

Multiply the number by 0.013. Add 0.06 to this new value to determine the gauge of the screw in inches.

Multiply the gauge of the screw in inches by 25.4 to convert the inches into millimetres. Write the screw size in the following format: (screw gauge in millimetres) | (screw length in millimetres).

Tip

Alternately, you can refer to a metric/imperial size conversion chart to check the size of your screw.

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About the Author

Alexander Poirier began writing professionally in 2005. He worked as the editor-in-chief of the literary magazine "Calliope," garnering the magazine two APEX Awards for excellence in publication. Poirer graduated from the University of the Pacific with a Bachelor of Arts in English.