How to Use a Ruler

Rulers are everywhere. You can find them in every classroom, office and workshop. Everybody knows the basics of using a ruler--how to measure something in inches or use them for a straightedge--but not everybody knows what all of the little marks actually mean on them. Nearly every ruler has the same breakdown of markings, so it's pretty easy to learn, as described here.

Instructions

1. Decide if you have a metric or an English ruler. Metric rulers have numbers every centimeter, and English have them every inch. Centimeters are much smaller than inches, so metric rulers will have a lot more numbers printed on them. If you still have trouble telling what type of ruler you have, centimeters are normally about as wide as one fingertip, and inches are about as wide as two.

2. Read an English ruler using fractions of an inch. The distance between any two large numbered lines is 1 inch. The large unnumbered line that is halfway between them is 1/2 inch. The smaller (but still prominent) line between the 1/2 mark and the numbered inch line is 1/4 inch. The tiny little lines between all of the more prominent lines are 1/16 inch.

3. Observe the much simpler metric rulers. The distance between any two large numbered lines is 1 cm. The prominent line between any two numbered lines is 1/2 cm. The small lines between the 1/2 mark and the numbered centimeter mark are 1/10 cm, otherwise known as a millimeter.

4. Record distances by the name of the line that it most closely matches. If the length of an object goes to one mark past the halfway mark on your ruler then it will be 9/16 inch on an English ruler or 6/10 cm (or 6 mm) on a metric ruler.

Tips & Warnings

• Regular-sized rulers are almost always a foot long, regardless of whether they are metric or English. There are some smaller rulers that are only 6 inches long. The much longer rulers are either 1 yard long (3 feet) or 1 m long (100 cm). It is sometimes difficult to tell which type you have, since a yard and a meter are very close in length.