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!