Length and units
Key points
mm, cm and m
1 cm = 10 mm, and 1 m = 100 cm. Use mm for tiny things, cm for everyday things, and m for rooms and buildings. You pick the unit to match what you are measuring.
The height is in mm. 1 m is 1000 mm, the same as 100 lots of 1 cm.
How to read a ruler
Line the end of the object up with the 0 on the ruler. If you start from 1 instead of 0, your answer comes out 1 cm short. A ruler works just like a number line.
Make the units match before you calculate
"Cut 40 cm off a 3 m paper tape" is not a subtraction you can do as it stands. First change 3 m into 300 cm, then work out 300 − 40 = 260 cm. Make the units match. That is the one thing you must never forget.
To compare, use the same unit
Which is longer, 150 cm or 1.4 m? Since 1.4 m = 140 cm, 150 cm is the longer one. Once both lengths are in the same unit, comparing them is easy.
Check yourself 5questions
Tap an option to check
Q1 How many cm are in 1 m?
Q2 You cut 40 cm from a 3 m tape. How much is left?
Q3 Which is longer, 150 cm or 1.4 m?
Q4 Which unit fits best for measuring the length of a pencil?
Q5 You lined the object up with the 1 on the ruler and read off 8. What is the real length?
Jobs that use this
Every job uses this. The ones below are just where it shows up most.
Carpenter / building tradesperson$58k
If a measurement is off by a millimeter, the door will not close. Without measuring carefully and keeping the units consistent, no house gets built.
Maths used: LengthUnitsArea
Clothing pattern maker$48k
They measure the body and draw the paper patterns the fabric is cut from. A few millimeters can change how comfortable a garment feels.
Maths used: LengthRatioShapes
Civil engineering and surveying technician$70k
They measure and record the length of roads and bridges down to the millimeter. Mixing up units here leads straight to serious accidents.
Maths used: LengthUnitsAngles
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