Rulers are useful tools, but sometimes we take for granted what they can do. That strip of wood, plastic, or metal isn't just for drawing straight lines. It can help you visualize and solve a math problem or draw a right angle. You can complete a construction project conceived in a foreign country or draw blueprints for an ambitious home improvement project. With a good understanding of how a ruler works, you'll basically be mathematically unstoppable.

01## Imperial or metric?

Your ruler measures objects using the imperial system, the metric system, or both — one unit of length on each side. Imperial measurements are inches, with smaller increments represented by fractions. In the metric system, millimeters and the larger centimeter (ten millimeters) are the standards, with increments recorded in decimals. The metric system is the worldwide standard, but you're more likely to encounter inches and feet in the United States.

02## Measuring by inches

Most standard inch rulers are 12 inches, or one foot, long, with each inch divided into sixteen sections. The lines separating each division are different lengths because they represent specific fractions. The long lines identify every inch, always a whole number, and the second-longest lines divide those into 1/2-inch segments. The third-longest lines represent 1/4-inch measurements, while the second-shortest lines bisect quarter-inches into 1/8th-inch increments. The shortest lines measure 1/16th-inch sections.

03## A metric ruler

The metric system is another way of measuring short distances, with standard rulers reaching 30 centimeters in length. The shorter lines on your metric system ruler represent the smallest unit of measurement, the millimeter. Every ten millimeters adds up to one centimeter, denoted by long lines and whole numbers. Each centimeter has a mid-length line bisecting it into halves, though you'll record measurements in decimals rather than fractions. A half-centimeter, for example, should be written as 0.5 centimeters.

04## Taking an accurate measurement

When measuring an object or distance with a ruler, first locate the zero line. Unlike a tape measure, a ruler has additional length at its end that, if unaccounted for, could provide inaccurate measurements. Align the zero mark with the edge of the object you're measuring, then read from left to right. The line that marks the end of the distance you're recording is your length. If it's on the division halfway between the nine- and ten-inch marks, your measurement is 9-1/2 inches. If it's two tiny lines past 13 on a metric ruler, your value is 13.2 centimeters.

05## Conversions

Maybe you found the perfect home improvement project online, but its dimensions are in the metric system. As long as you can record precise lengths in either metric or imperial measurements, conversions are easy to calculate using a fraction and decimal conversion chart. You might be able to do the math on your own, but using a cheat sheet is fast and reliable when your attention is needed on other tasks. Online calculators also do the trick.

06## Standard Rulers

Most people can get by with a standard desk ruler for measuring everyday distances and drawing straight lines. For objects greater than 12 inches or 30 centimeters, a yard or meter stick is more appropriate. A steel ruler is more durable, and its thinner, flatter construction allows you to more accurately draw lines. Flexible plastic rulers are best for measuring uneven or curved surfaces.

07## Arts and engineering

Set squares are a popular tool in the artist's or engineer's toolbox, though the name is a bit misleading. These rulers are triangle-shaped with the center cut out, providing several straight edges. They are perfect for making parallel and perpendicular lines as well as right angles and 30- and 60-degree angles. Parallel glider rulers draw more precisely angled and spaced lines. Add a protractor, and you've got an ideal artist's starter pack.

08## The best housewarming gift

A speed square is a multitasking tool that makes a perfect housewarming gift. Besides taking standard measurements, it also helps you find and draw accurate angles using a pivot point on one end. One edge of the speed square has a firm lip that stabilizes it while you take measurements or as you guide a circular saw in a straight line. Notches on the inner edge help you scribe straight lines on timber and also make a great impromptu bottle opener.

09## Industry professional rulers

A steel machinist's scale ruler is perfect for mechanics and similar shop professionals who need precise measurements. The tool features 1/16th-inch increments on one side and 1/32nd-inch increments on the other. Hook rulers come with a catch at the end for accurately lining up the zero point without the added bulk of a tape measure. Calipers measure the inside or outside diameters of cylinders, pipes, and openings.

10## The carpenter's secret weapon

Carpenters might use tape measures on the job, but it isn't uncommon to see the occasional yardstick or folding ruler in the workshop. Usually made of wood or steel, folding rulers are handy for making angles, transferring angles, or drawing impromptu circles. T-squares are also useful for carpenters, architects, and other professionals in drafting and planning.