How to Read a Measuring Tape in Centimeters and mm

The three metric units on a tape

Metric tapes are built on tens, so the math is easier than with fractions of an inch. You only need to know how the three common units relate.

The numbered lines are usually centimeters (cm). The smallest lines between them are millimeters (mm). Meters (m) are the big jumps, and many tapes make those marks longer or label them differently.

Which side of the tape is centimeters

Most tapes put inches on one edge of the blade and metric on the other. The two scales run along the top and bottom of the blade, so flip the tape and look at both edges.

Look for a small "cm" or "mm" label near the start of the blade. The metric scale also has a different rhythm. Its numbers count up quickly, while inch numbers climb more slowly across the same blade length.

Some tapes print a second scale on the back of the blade instead. The Klein Tools 9225 lists measurement scales on both the front and back of its blade, so check both sides before you assume a tape has no metric scale. The Amazon Basics 16 ft tape lists both inch and metric markings, and it is described as a 16-foot (5-meter) tape.

How to read centimeters and millimeters step by step

Once you know which edge is metric, the reading is the same every time. Take your time with the first few measurements, and it will soon become automatic.

• Hook the end of the tape on the edge of what you are measuring, and pull the blade straight along it.
• Find your endpoint on the metric edge.
• Read the last numbered line before the endpoint. That is your whole centimeters.
• Count the small lines between that number and your endpoint. Each one is 1 mm.
• Add the two together, for example 47 cm plus 3 mm is 47.3 cm, or 473 mm.
• Check that the blade is straight and not sagging, because a bent blade reads long.

Worked examples with mm, cm and meters

Say your endpoint lands three small lines past the 47 line. That is 47 cm and 3 mm. In centimeters you write 47.3 cm, and in millimeters you write 473 mm.

Many tapes also have a longer line halfway between two centimeters, which is the 5 mm mark. If your endpoint sits right on that line, you have 5 mm past the last whole centimeter. A mark on the 12 cm line plus the half line is 12.5 cm.

For longer lengths, the numbers often keep climbing past 100. If your endpoint is 6 mm past the 123 line, that is 123.6 cm. Divide by 100 to get meters, so 123.6 cm is 1.236 m, or 1 m, 23 cm and 6 mm. Some tapes also print a separate meter marker, so check what yours does at 100 cm.

To convert quickly, remember these shortcuts:

• mm to cm: divide by 10, so 250 mm is 25 cm.
• cm to mm: multiply by 10, so 8.4 cm is 84 mm.
• cm to m: divide by 100, so 340 cm is 3.4 m.
• m to cm: multiply by 100, so 2.5 m is 250 cm.

Common mistakes and how to avoid them

The most common error is reading the wrong edge. If a number looks far too large or too small, flip the tape and check that you are on the metric side.

The second is the hook. The metal tip at the end of the blade is designed to slide a little, so it is accurate whether you push it against a surface or hook it over an edge. Keep it clean and straight, and do not bend it.

Another slip is counting the small lines. Count from the last numbered centimeter, not from the one after your mark. If you are unsure, read the line on each side of your mark and decide which is closer.

Finally, measure twice. Write the unit next to every number, such as "63.5 cm" instead of just "63.5", so you do not mix centimeters with millimeters later.

Choosing a tape that is easy to read in metric

If you measure in metric often, look for a tape with clear, bold lines and a metric scale you can find at a glance. A wider blade can make small marks easier to see. In our lineup, the STANLEY FATMAX lists a 1.25 in blade, the widest listed, while the Klein Tools 9225 lists bold lines marked every 1/8 inch on the inch side.

Blade length matters for the units you work in. A 16 ft tape such as the Amazon Basics model covers about 5 meters, which suits rooms and furniture. For longer runs, a 25 ft blade gets you further in one pull. You can compare these specs line by line on our best measuring tape page.

If a tape lists inch scales only, or does not mention metric at all, check the product details before you buy it for centimeter work. Our measuring tape comparison notes which ones list both scales, so you can pick one that matches how you measure.

Safety notes when you measure

A tape blade can snap back fast and its edge can cut skin, so keep your fingers clear of the blade as it retracts and guide it back by hand. Some tapes have a brake or lock that slows retraction, which helps.

The blade is metal and conducts electricity. Never extend a tape near live wires, outlets or panels, and do not use one on energized equipment.

If you measure overhead, use a stable ladder and keep your balance. Do not reach out or lean to pull the blade farther. If you cut material to your measurements, wear eye protection for the cutting step.

Frequently asked questions

How many millimeters are in a centimeter?

There are 10 millimeters in each centimeter. The ten small spaces between two numbered centimeter lines show this.

How do I read a tape in meters?

Read the centimeters first, then divide by 100. For example, 215 cm is 2.15 m. Some tapes also print a marker at each full meter.

Can I measure mm if my tape has no millimeter lines?

Not reliably. If the tape only shows centimeters, you can estimate halves, but you cannot read true millimeters. Use a tape or ruler with mm lines for precise work.

Why does my tape show both inches and centimeters?

Dual-scale tapes let you switch units without converting. The two scales sit on opposite edges of the blade, or on the front and back.