Speed converter

Five units of speed at once. The two worth carrying in your head: 100 km/h is about 62 mph, and a knot is about 1.15 mph.

The knot is a nautical mile per hour, and since a nautical mile is one minute of latitude, a vessel making one knot covers one minute of latitude an hour — which is what made it worth having before satellites. Aviation and shipping still use it for the same reason. For everyday road work, the useful approximation is that km/h to mph is roughly divide by eight and multiply by five: 80 km/h becomes 50 mph, which is accurate to within about one percent and does not need a calculator.