How to Read mm on a Ruler
- 1). Examine the metric ruler. The longer numbered hash marks are the centimeters. Count the hash marks between two whole numbers to see that the centimeters divide into ten increments. Each of these increments is a millimeter (mm).
- 2). Lay the ruler against a small object such as a crayon or a playing card, lining up the end with the edge of the object. Count how many whole numbers, four, for example. This indicates the centimeters. Since you know that there are 10 millimeters (mm) in every centimeter, you can multiply the centimeters by 10 to calculate that for centimeters equals 40 millimeters.
- 3). Count the intermediary hash marks past the last whole number, for example seven. Each hash mark represents one millimeter, so you can read that as seven millimeters or 0.7 centimeters.
- 4). Combine the two and you get a measurement of four centimeters seven millimeters, 4.7 centimeters or 47 millimeters.