How to Read a Ruler: Inches, Fractions, Centimeters and Millimeters
Updated
Reading the inch side
An inch ruler divides each inch into 16 parts. The tick length tells you the fraction:
- Longest tick: whole inch
- Second longest: 1/2 inch
- Next: 1/4 and 3/4
- Next: the eighths (1/8, 3/8, 5/8, 7/8)
- Shortest: the sixteenths
To read a length, count the whole inches, then count the sixteenths past the last whole inch and simplify. Ten sixteenths becomes 5/8, so the reading is, for example, 2 5/8 inches.
Reading the metric side
On a centimeter ruler, numbered ticks are centimeters and the nine short ticks between them are millimeters, with a slightly longer tick at 5 mm. 4 numbered ticks plus 7 short ticks is 4.7 cm, or 47 mm.
Converting between them
1 inch is exactly 2.54 cm. Multiply inches by 2.54 to get centimeters, or divide centimeters by 2.54 to get inches. 1/16 inch is about 1.6 mm, and 1 mm is about 1/25 inch.
Practice on screen
Open the online inch ruler and tap anywhere: the readout shows the decimal and the nearest 1/16 fraction, so you can check your reading instantly.
Measure it now with the free actual-size ruler.
Open the ruler