How to Read a Ruler in Inches and Centimeters
Most rulers have two scales: inches on one edge and centimeters on the other. Once you know what each line means, reading either takes seconds.
Reading the inch scale
An inch is usually split into 16 parts. The longer the line, the bigger the fraction:
| Line | Means |
|---|---|
| Numbered, longest | Whole inch |
| Second longest | 1/2 inch |
| Third | 1/4 inch |
| Fourth | 1/8 inch |
| Shortest | 1/16 inch |
Example: an object ends 5 short lines past 1 inch. Each shortest line is 1/16, so it is 1 and 5/16 inches. If it ends on the 1/4 line, it is 1 and 1/4 inches, which is the same as 1 and 4/16.
Tip: always simplify. 8/16 is 1/2, 4/16 is 1/4, 2/16 is 1/8.
Reading the metric scale
- Numbered lines are centimeters.
- The middle line between two numbers is 5 mm.
- Small lines are single millimeters, 10 per centimeter.
Example: an object ends 7 lines past 4. That is 4.7 cm, or 47 mm.
Converting between them
- Inches to cm: multiply by 2.54.
- cm to inches: divide by 2.54.
- 1/16 inch is about 1.6 mm, so the metric scale is slightly finer.
Practice on screen
Open the inch ruler or the cm ruler, drop two guides on the edge and compare your reading with the distance label. It is a quick way to learn the scale.