DIY 101: How To Properly Read a Tape Measure

Any DIYer on almost any project would be wise to follow the traditional carpenter’s advice: “Measure twice; cut once.” Even seasoned pros remind themselves to do this. For new DIYers, it means learning the ins and outs of a tape measure, that skinny strip of metal covered with tiny lines and numbers.

A few quick tips can help you get comfortable with this all-important DIY tool and ensure you always cut just once.

Tape Measure Basics

A tape measure is a really simple tool. Most have four main elements:

• Case: The box that holds the coiled tape. Most include a clip for hanging the tool onto a belt. Almost all have a measurement printed at their bottom edge that tells you exactly how wide the case is. This allows you to take an interior measurement, such as inside a window frame, and use the case as part of the measurement. This way you can take an accurate reading without bending the tape into the corner of the frame and guessing.
• Tape: The slightly curved, flexible metal tape with markings for inches, feet and fractions of inches. Some tapes offer standard (Imperial) and metric markings.
• Hook: The metal piece loosely fastened to the end of the tape for hooking onto the end of a board, etc. Note that the hook slides back and forth slightly. This movement compensates for the thickness of the hook, ensuring you get the same measurement whether you’re pulling the tape from the edge of the material or pushing the hook into a corner.
• Lock: A lever or thumb-slide mechanism that, when engaged, prevents the tape from retracting. Use the lock when you need to mark multiple measurements on the same piece.

How To Read a Tape Measure

The easiest tape measure to read has standard scales on both sides of the tape, with no metric marks. A good example is the builder’s perennial favorite, the Stanley PowerLock. The 25-foot version is the most versatile and easier to read than smaller tapes. But metric scales can be helpful for detailed work, with no fractions to deal with.

Reading standard tapes

The trick to reading standard tapes is learning to recognize the markings from largest to smallest. Most standard tapes have a special mark, such as an arrow, at each foot. Inch marks have a full line. Half-inch marks are the next longest, followed by 1/4-inch, 1/8-inch and 1/16-inch. Some tapes have 1/32-inch marks, but these can be tedious to read.

If you need more precision than 1/16-inch, do what builders do and note a slight adjustment with terms like “take the line” (meaning take a bit more off when you cut) or “plus a hair” (meaning add a hair’s width the measurement, or about 1/32-inch).

For most measurements, focus on inches and fractions of inches. Don’t bother with feet because it adds an unnecessary number. It’s simpler to note a 10-ft. 2-in. board is 122 inches. The tape measure tells you this, so no math is required.

For fractions of inches, it can help to count up or down from the larger marks. One mark to the left of the 1/2-in. line is 7/16; one mark to the right of the 7/8-in. mark is 15/16.

It can also help to spend a moment studying your tape and remembering fraction conversion:

• 3/4 = 12/16;
• 1/2 = 8/16;
• 1/4 = 4/16;
• 1/8 = 2/16.

Reading metric tapes

The nice thing about these? You only need one number (in millimeters), and the gradations are small enough that you don’t need to parse them. While a standard tape reading might be “7-3/8-in., plus a hair,” the same measurement in metric would be “188 mm.”

Metric tapes show centimeters. Between the centimeter lines, nine marks indicate millimeters. The middle one is long to indicate 5. One centimeter equals 10 millimeters, so you multiply the numbers on the tape by 10 to find the millimeters. So 12 centimeters equals 120 millimeters.

Most measurements are taken in millimeters. Start with the nearest centimeter number and count the millimeters to the right. If a board measures 50 centimeters plus three little marks, the dimension is 503 millimeters.

Tape Measure Tips

A few pieces of advice on tape measure use and care:

• Use an easy-to-read tape measure. Simple standard tape measures have a clean look and include identical markings on both edges of the tape, so you can read them along the top or bottom.
• Burn an inch. When precision counts (or your tape is getting old and the hook loosens, throwing off your measuring), start your measurement on the 1-in. mark, then subtract an inch from the total measurement. So if you burn an inch and your board measures 23 inches, the actual dimension is 22 inches.
• Mark with a crow’s foot. Take a cue from pro carpenters and mark your measurements with a little V shape, AKA a crow’s foot, instead of drawing a little straight line (which isn’t always as straight as you think). A crow’s foot is like an arrow, and its point indicates the measurement. If you’re cutting a board to length at 23 inches, make a crow’s foot with its point at 23 inches. Then draw a cutting line through the point of the crow’s foot with a square and pencil.
• Use a mechanical pencil (or sharpen often). Most builders use carpenter’s pencils. But you have to sharpen these flat-sided pencils frequently, and it’s tricky to do. For DIYers, a simple mechanical pencil like a classic Bic pencil always makes a clean line and never needs sharpening. Never use a marker unless you’re working with plastic or metal sheets, and make sure it’s an ultra-fine Sharpie.
• Take care of your tape. Keep the blade clean and retract it after each measurement so it can’t get stepped on. Carry it in a tool pouch or clipped on your belt; don’t just toss it into a bucket or toolbox. If it develops a permanent kink or if the lock no longer works, replace the tape. And if you drop it on a hard surface, check the hook right away. If it’s bent, it’ll throw off all your measurements unless you burn an inch (see above).