Understanding the topic
A tape measure is useful only when you understand its markings and read from the correct starting point. Metric tapes typically show centimetres with ten millimetre divisions. Some tapes also include inches divided into fractions.
Quick reference
Use these reference points alongside the worked examples below.
| Term | Meaning / value | Why it matters |
|---|---|---|
| 10 mm | 1 cm | Ten millimetres make one centimetre |
| 100 cm | 1 m | One hundred centimetres make one metre |
| 25 mm | 2.5 cm | Useful for small fittings |
| 1/2 inch | 12.7 mm | An approximate half-inch equivalent |
| 1/4 inch | 6.35 mm | A common imperial fraction |
Step-by-step method
- Check whether you are reading the metric or imperial scale.
- Place the tape hook against the starting edge without twisting the tape.
- Keep the tape straight and level along the object.
- Read the last whole centimetre and count the millimetre marks after it.
- Record the number with its unit and measure again to confirm.
Worked examples
Example 1: Shelf width
A shelf ends three small marks after 42 cm. Its width is 42.3 cm or 423 mm.
Example 2: Door opening
Read 810 mm at the narrowest point, then measure the top, middle and bottom to check for variation.
Example 3: Converting centimetres
A measurement of 175 cm is 1.75 m because 175 ÷ 100 = 1.75.
Common mistakes and useful cautions
- Confusing the centimetre numbers with millimetres creates a tenfold error.
- Measuring diagonally instead of straight can overstate a width.
- Bent hooks and damaged tapes can affect accuracy; check the zero point.
Practice questions
Try each question before revealing the answer.
Question 1: What is 68 mm in centimetres?
Answer: 6.8 cm.
Question 2: A tape shows 23 cm plus 7 mm. What is the measurement?
Answer: 23.7 cm or 237 mm.
Question 3: Why measure a doorway in three places?
Answer: The opening may not be perfectly square or uniform.
What to remember
- Check whether you are reading the metric or imperial scale.
- Record the number with its unit and measure again to confirm.
- Confusing the centimetre numbers with millimetres creates a tenfold error.