How to read a tape measure

To read a tape measure, find the last whole inch the blade passes, then count the small lines past it. On most US tapes each small line is 1/16 inch, so 5 lines past the 3 reads 3 5/16 inches. Longer lines mark the bigger fractions (1/2, 1/4, 1/8), which lets you read most measurements at a glance without counting every line.

Point anywhere on the tape above to see the reading and check yourself as you learn.

The inch marks, from longest to shortest line

A standard US tape divides each inch into 16 parts. The length of each line tells you which fraction it marks. The longer the line, the bigger the fraction.

• Inch line. The longest line, with the inch number printed next to it.
• 1/2 inch. The next longest line, exactly halfway between two inch numbers.
• 1/4 inch. Slightly shorter lines at the 1/4 and 3/4 points.
• 1/8 inch. Shorter again, halfway between each quarter mark.
• 1/16 inch. The shortest lines, between every pair of eighth marks.

Some tapes mark 1/32 inch along the first few inches for close work. The rest of the blade, and most DIY tapes, stop at 1/16.

Counting sixteenths and reducing the fraction

When the line you need is not an obvious half or quarter, count sixteenths. Start at the last whole inch and count each small step to your mark. That count is the top number of the fraction, and 16 is the bottom.

Then reduce it. Plans, cut lists and carpenters all use the reduced form, so 10/16 is written and spoken as 5/8. If the top number is even, divide the top and bottom by 2, and keep going until the top number is odd.

• 4/16 becomes 2/8, then 1/4
• 6/16 becomes 3/8
• 10/16 becomes 5/8
• 12/16 becomes 6/8, then 3/4
• 7/16 stays 7/16, because 7 is odd

With practice you will skip the counting. A mark one line past the 1/2 is 9/16. A mark one line short of the 3/4 is 11/16. Use the long lines as landmarks and count only the last step or two.

Feet on a tape measure

Inch numbers on most tapes keep running past 12, so you will see 13, 14, 15 and so on up the blade. To help with feet, most tapes add a foot marker every 12 inches. It is often a highlighted box or a label such as 1F, 2F or 1’, 2’. Some tapes also print feet and inches in small type next to the inch number, so 13 also reads 1’ 1”. The exact style varies by brand.

To convert inches to feet yourself, divide by 12. A reading of 50 inches is 4 feet (48 inches) plus 2 inches, written 4’ 2”.

Many tapes also highlight every 16 inches in red and add small black diamonds at 19.2-inch spacing. Those are framing layout marks. The tape measure markings guide explains each one.

Worked example: reading a measurement

Say you are measuring a shelf board. Hook the end of the tape over one edge and pull the blade flat along the board to the other end.

1. Look at where the board ends on the blade. The last whole number it passed is 37.
2. The end of the board lines up with a line past the 37. It is two lines beyond the 1/2-inch mark.
3. Count from 37. The 1/2 mark is 8 sixteenths, so two more makes 10 sixteenths.
4. Reduce 10/16 to 5/8.
5. The board is 37 5/8 inches long, or 3’ 1 5/8”.

If the edge falls between two lines, read it to the nearer one. For rough work, round to the nearest 1/8. For trim, cabinets and anything that has to fit tight, stay with the nearest 1/16.

The metric side (centimeters and millimeters)

Many tapes sold in the US carry a metric scale along the bottom edge, and tapes sold elsewhere are often metric only. Reading it is simpler because everything is in tens.

• The numbered lines are centimeters (cm).
• Each small line between them is 1 millimeter (mm). There are 10 mm in 1 cm.
• The slightly longer line halfway between two numbers is 5 mm.
• Meters are usually marked at 100, 200 and so on, often in red or with a label such as 1M. Styles differ between brands.

To read it, take the last centimeter number and add the millimeter lines past it. Four lines past the 23 is 23.4 cm, which is 234 mm. Builders and cabinet makers working in metric usually write everything in millimeters, so a board of 1 m 23.4 cm is noted as 1234 mm.

The shelf from the example above, 37 5/8 inches, is about 955.7 mm, or 95.6 cm. One inch equals exactly 25.4 mm.

Tape measure fractions chart

Use this table to turn any sixteenth into a decimal inch or millimeters. Millimeters are rounded to two decimal places.

Sixteenths	Fraction	Decimal inch	Millimeters
1/16	1/16	0.0625	1.59
2/16	1/8	0.125	3.18
3/16	3/16	0.1875	4.76
4/16	1/4	0.25	6.35
5/16	5/16	0.3125	7.94
6/16	3/8	0.375	9.53
7/16	7/16	0.4375	11.11
8/16	1/2	0.5	12.70
9/16	9/16	0.5625	14.29
10/16	5/8	0.625	15.88
11/16	11/16	0.6875	17.46
12/16	3/4	0.75	19.05
13/16	13/16	0.8125	20.64
14/16	7/8	0.875	22.23
15/16	15/16	0.9375	23.81
16/16	1	1.0	25.40

Common mistakes

Reading the next number instead of the last one. If the blade ends between 37 and 38, the reading is 37 and a fraction. People often glance at the closest printed number and write 38. Always start from the whole inch you have already passed.

Reading from the wrong side or the wrong scale. On a tape with inches on top and centimeters on the bottom, it is easy to read a centimeter line as an inch fraction. Check which edge you are using. Also read the tape so the numbers count up away from the hook. If you read the blade upside down, a reading of 6 and a bit can look like 9 and a bit.

Pressing the hook flat or forgetting it slides. The hook at the end is loose on purpose. It slides out by its own thickness when you hook it over an edge and pushes in when you butt it against a wall. That movement keeps both readings correct. If the hook is bent, or the rivets are worn from snapping the blade back into the case, every measurement will be off by the same small amount.

Ignoring sag and angle. Over a long span the blade droops, which adds length. Keep it tight and straight, and measure square to the edge. A tape laid at a slant across a board reads longer than the board is.

Guessing inside measurements. For the inside of a window frame or between two walls, the tape cannot bend into the corner. Butt the case against one side and add the case length, which most tapes print on the back of the case. The window measuring guide walks through this in detail.

Using a worn first inch for fine work. For close cuts, some carpenters burn an inch. They line up the 1-inch mark with the edge instead of the hook, then subtract 1 inch from the reading. It avoids any play in the hook. Forgetting to subtract the inch is the classic error with this method.

Without a tape, our guide to measuring without a tape measure covers everyday objects you can use as a reference, and the AR ruler app gives a close estimate with your iPhone camera. For short pieces under a foot, a ruler is often easier to read than a tape, and the same rules apply. See how to read a ruler.