EngineerBenchConverting fractional inches and metric lengths
An inch is exactly 25.4 millimeters. This length converter accepts decimals, fractions, and simple arithmetic, so a drawing dimension such as 2 + 3/8 can be entered directly. Choose the starting unit and the required unit before copying the converted dimension.
Write mixed fractions explicitly
Use a plus sign between the whole number and fraction: 2 + 3/8 rather than 2 3/8. Parentheses can make a compound expression clearer. The units are chosen in the controls; the numeric field is for the measurement itself.
Conversion does not add measurement accuracy
An exact conversion factor does not make the original measurement more precise. Keep enough digits for the next calculation, then round the final drawing or inspection value to a suitable precision. For area, volume, or other quantities, use the general unit converter.
Reading a fractional drawing dimension
A dimension of 2 + 3/8 inches is 2.375 inches. Multiplying by the exact 25.4 mm per inch gives 60.325 mm. The plus sign makes the intended mixed fraction explicit; entering 23/8 would instead mean 2.875 inches. When checking a drawing, confirm that a fraction bar or a space has not been lost while copying the value.
Convert nominal dimensions and tolerance limits consistently. A dimension of one inch with a tolerance is not the same as an exact one-inch definition with unlimited measurement precision. If a shop works to millimeters, convert both the upper and lower limits before choosing an appropriate reporting precision. Rounding too early can move a limit enough to change acceptance near an endpoint. This tool converts length expressions, not screw-thread designations or pipe-size names. A nominal inch label on a purchased component can refer to a size series rather than its measured dimension, so use the relevant drawing when an actual measurement is required.
Formula
Multiply by the exact unit conversion factor.