Useful Imperial fraction to metric conversions
I’ve been having to do a lot of fiddly metric conversions recently. The imperial system is such a mess, especially that random mix of fractions and decimals that you often see for smaller measures.
So if I'm working on a project that's scaled down from imperial measurements, I always try to get materials at the nearest metric equivalent. But converting from fractions involves two numeric steps, which is a minor nuisance.
To save time I've slapped together a simple table of linear imperial fraction measurements to metric measurements. The measurements in blue are useful ones that come close to whole unit millimetre measurements. Note there are some goofy fractions here that you never see mainly for completeness.
I’ve made it publicly available in case it’s useful to anyone else.
1/128" 0.0078" 0.198mm
0.0098" 0.25mm
1/64" 0.0156" 0.397mm
0.020" 0.508mm
3/128" 0.0234" 0.595mm
0.0295" 0.75mm
1/32" 0.0313" 0.793mm
5/128" 0.039" 0.99mm (ie: 1.0mm)
3/64" 0.0469" 1.19mm
1/16" 0.0625" 1.59mm
0.072" 1.829mm
5/64" 0.0781" 1.984mm (ie: 2.0mm)
0.081" 2.06mm
3/32" 0.094" 2.38mm
7/64" 0.1094" 2.778mm
0.114" 2.896mm (ie: 3.0mm)
0.118" 3.0mm
1/8" 0.125" 3.175mm
9/64" 0.141" 3.572mm
5/32" 0.1563" 3.97mm (ie: 4.0mm)
11/64" 0.1719" 4.365mm
3/16" 0.1875" 4.76mm
0.1969" 5.0mm
13/64" 0.203" 5.16mm
7/32" 0.219" 5.56mm
15/64" 0.234" 5.953mm (ie: 6.0mm)
1/4" 0.25" 6.35mm
17/64" 0.266" 6.747mm
9/32" 0.2813" 7.14mm
19/64" 0.2969" 7.54mm
5/16" 0.313" 7.94mm (ie: 8mm)
21/64" 0.328" 8.334mm
11/32" 0.344" 8.73mm
23/64" 0.359" 9.128mm
3/8" 0.375" 9.525mm
25/64" 0.391" 9.92mm (ie: 10mm)
13/32" 0.406" 10.32mm
27/64" 0.4219" 10.72mm
7/16" 0.4375" 11.11mm
29/64" 0.453" 11.51mm
15/32" 0.469" 11.91mm (ie: 12mm)
31/64" 0.484" 12.3mm
1/2" 0.5" 12.7mm
17/32" 0.53" 13.49mm
9/16" 0.5625" 14.29mm
19/32" 0.5938" 15.08mm (ie: 15mm)
5/8" 0.625" 15.875mm
21/32" 0.656" 16.67mm
11/16" 0.6875" 17.46mm
23/32" 0.719" 18.256mm
3/4" 0.75" 19.05mm (ie: 19mm)
25/32" 0.781" 19.84mm
13/16" 0.8125" 20.64mm
7/8" 0.875" 22.23mm
29/32" 0.906" 23.02mm
15/16" 0.9375" 23.81mm
1" 1.0" 25.4mm
1 1/4" 1.25" 31.75mm
1 1/2” 1.5" 38.1mm
1 3/4" 1.75" 44.45mm
2" 2.0" 50.8mm
Finally, some thou (1/1000 inch, often called mils in the US) conversions, since Americans like to use that for stuff like sheet styrene.
1 thou 0.0254mm
2 thou 0.0508mm
3 thou 0.0762mm
4 thou 0.1016mm
5 thou 0.127mm
6 thou 0.1524mm
7 thou 0.1778mm
8 thou 0.2032mm
9 thou 0.2286mm
10 thou 0.254mm (ie: 0.25mm)
20 thou 0.508mm (ie: 0.5mm)
30 thou 0.762mm (ie: .75mm)
40 thou 1.016mm (ie: 1mm)
60 thou 1.524mm (ie: 1.5mm)
80 thou 2.0574mm (ie: 2mm)
120 thou 3.048mm (ie: 3mm)
Still, as bad as this is, it's not quite as nonsensical as the gauge system for stuff like metal thickness and diameter, where totally different and non-linear gauge numbers apply to different types or shapes of metal. (eg: plain carbon steel has a different “gauge” from stainless steel or aluminium)
Given that there are over 50 types of gauge systems out there (they still use AWG, or American Wire Gauge in the US), it's as bad as building a mediaeval castle and basing the measurement system on the length of the local king's foot!