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Whether you're working with inches or centimeters, reading a ruler is a simple task. Javier Zayas Photography / Getty ImagesA ruler — typically made from wood, plastic, or metal — is essential for measuring objects and is also great for drawing straight lines in geometry class. But are you familiar with how to properly read a ruler?
Various Types of Rulers
In the U.S., rulers are commonly 12 inches (30.48 centimeters) long, with larger marks indicating inches and smaller ones for fractions of an inch.
Other countries predominantly use the metric system, which measures length in millimeters, centimeters, and meters. The U.S., Liberia, and Myanmar are the only nations that use the imperial system by default.
The United Kingdom utilizes both measurement systems, and many British rulers feature inches on one side and centimeters on the other.
How to Read a 12-Inch Ruler
Using a ruler is straightforward. Here’s a simple guide to using and reading a U.S. or British ruler.
- Position the object you wish to measure with its end at the zero mark, which is on the left side of the first inch mark.
- The longest lines on the ruler indicate inches. These lines are numbered. If the object ends exactly at one of the inch marks, it is that many inches long. For instance, if it ends at the first inch mark, it measures one inch.
- If the object falls between two long lines, you will need to measure the fraction of an inch between them.
- The second longest lines represent half an inch, placed exactly in the middle of two inch marks. The line between the inch and half-inch lines is a quarter-inch. The smallest lines on a standard ruler show 1/16 inch.
How to Use a Metric Ruler
Countries and sectors that use the metric system rely on metric rulers, which measure in centimeters and millimeters. Reading a metric ruler is similar to using an inch ruler, but the smaller lines represent millimeters rather than fractions of an inch marked by varying lengths.
- Place the end of the item you want to measure at the zero mark, which is usually labeled "0 cm."
- The longest lines on the ruler mark each centimeter. The space between each of these lines represents one centimeter.
- The shorter lines are millimeter markings. There are 10 millimeters in a centimeter, so the fifth line between two centimeter marks shows half a centimeter, or 5 millimeters.
- The 5-millimeter mark may be longer than the others, making it easier to count. Instead of counting all six millimeter lines, you can count five and add one.
Rulers work great for measuring small, flat items, but for larger objects requiring precise measurements, a tape measure is a better tool. Tape measures are flexible and function just like a ruler, but they can measure much larger items due to their ability to roll up.
