What is 5.5 mm in a ruler?

5.5 mm on a ruler is slightly more than half a centimeter, as 1 centimeter equals 10 millimeters. On a standard metric ruler, you can find 5.5 mm by locating the 5 mm mark and then measuring halfway between the 5 mm and 6 mm marks. It's important to use the millimeter side of a ruler for accurate measurement.