How to Read a Ruler

This little measuring device is not called “ruler” for nothing. Throughout the centuries, it ruled the building plans of the world’s great edifices from the pyramids of Egypt to the towering skyscrapers of New York. Without it, you would neither be able to find your house livable nor be able to comfortably fit into your clothes or shoes.

Tape measures, folding rulers, tape rules and yard sticks are just some of the many types of measuring devices that engineers, architects, shoe makers, tailors, graphic and web designers find indispensable in their jobs. Learning how to read a ruler enables you to acquire a valuable skill that gives you the edge on and off the job.

Rulers involve either the metric or English measurements. It is easy to read a metric ruler as it deals only with centimeters and millimeters. Ten millimeters is equivalent to one centimeter and one hundred centimeters equals one meter. Since a millimeter is 1/10th of a centimeter and a centimeter is 1/100th of a meter, 15 millimeters is 1.5 centimeters, or 5 marks after a centimeter while 150 centimeters can be read as 1.5 meters.

Learning how to read an English ruler, on the other hand, is much more challenging because it deals mostly with fractions. The longest segment in a typical ruler is an inch, which is marked by a line and a number, where 12 inches is equal to one foot. But what makes it particularly confusing is that the shorter segments are only marked by lines and not numbers. The short lines between inches represent sub-inches and the longer the line, the higher is the measurement. An inch is divided into 8 equal segments, where each segment marked by a short line represents 1/8th of an inch. And, each 1/8th segment is further sub-divided into two segments marked by the smallest line representing 1/16th of an inch.

Four 1/8th segments is read as 4/8ths of an inch, which when reduced to its lowest denominator, is equal to 1/2 of an inch. Similarly, eight 1/16th segments, which are read as 8/16ths of an inch, is commonly expressed as 1/2 of an inch when reduced to its lowest denominator. Six 1/8th segments or 6/8th, which is equal in length to twelve 1/16th segments or 12/16th, can be expressed as 3/4th of an inch when reduced to their lowest denominator. Other fractions which cannot be further reduced to their lowest denominator like 3/8th, 5/8th, 3/16th or 9/16th are expressed as such.

Thus, a measurement of one inch and six 1/8th segments or twelve 1/16 segments can be expressed as 1-3/4th inches. One bright spot in learning how to read a ruler is that for ordinary day-to-day application, the smaller segments are commonly rounded to the nearest inch to provide an allowance for the object being measured. Today, only engineers, architects, building contractors and craftsmen consider even the smallest segments of a ruler because of the exacting nature of their jobs.