Woodworkers' Popup Units Conversion Tool

Luthiers and woodworkers in general are forever converting back and forth between SI and US customary system (USCS) units of measurement. This page provides documentation for the popup units conversion tool which appears on this site.

Initially appeared: June 05, 2012
Last updated: September 11, 2018

The woodworkers' popup units conversion tool can be accessed via the box appearing in the right column of any page on this site. Typing a value into the text field in the box and then clicking on the button will invoke the popup tool with the value entered converted into millimeters, inches with decimal fraction, and inches with standard woodworking vulgar fraction. You can also just click on the button to invoke the tool, where you can enter a value to be converted directly.

The tool needs to know what units to convert from, so what you type (or paste) into its input field should contain both a number and units, such as:


The tool knows about inches (in, ", '', ”), millimeters (mm), centimeters (cm), feet (ft, ') and meters (m). If you indicate any other units or if you don't specify units at all it will just assume the input value is in inches.

Since the tool is intended for use by woodworkers, all values output are rounded off sensibly for woodworking use. Millimeters are rounded off to one decimal place. Decimal fraction inches are rounded off to three decimal places, and fractional inches are rounded off to the nearest 64th. So you can also use the tool to round down numbers if you wish. But be aware that the rounding means that very small values can be rounded to zero.

Note that you can enter fractional inches into the input field, like this:

12 7/8

Also be aware that you can enter unconventional fractional inches, like:

4 5/12

and the tool will convert them to conventional woodworking fractions in the output. This turns out to be of some use to folks that have antique plans, which often have oddball fractions in them.

The tool will accept negative values, but will not accept fractions where the numerator is equal to or larger than the denominator. It will gripe if you try to enter things it can't readily make sense of, but it doesn't provide any detailed information about just what it is griping about.


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Woodworkers' Popup Units Conversion Calculator

Calculator converts to/from decimal inches, fractional inches, millimeters. Popups must be enabled for this site.
Did you know....
.... you can click on most of the assembly photos on this site to enlarge them for a close look? Also, hovering the cursor over most linear dimension values will convert the values to decimal inches, fractional inches, and SI units.