While surfing the internet today, I realized I have a piece of lumber at home that was recently surfaced to 40 mm.
"How much is that in inches?" I asked myself.
A quick google came up with this site, and the answer of 1 9/16".
Just put in your mm or cm measurement, and out comes something useful for the shop. This is handy for those of us in Europe who prefer to use inches. Also, if you would like to use a plan in the shop that is metric.