Length: rulers, tape measures and problems
mm, cm, m and km: choosing the right unit, measuring and converting. Word problems with length: same unit first, then calculate. Read one part at a time and tap “I know this”. Then test yourself in the quiz.
Know it already? Jump straight to the quiz
Units of length
| Unit | Use for … | Convert |
|---|---|---|
| mm | very small: an ant | 10 mm = 1 cm |
| cm | a pencil, a book | 100 cm = 1 m |
| m | a room, a sports field | 1 000 m = 1 km |
| km | distances between towns |
Big to small unit: multiply (3 m = 300 cm). Small to big unit: divide (2 500 m = 2,5 km).
Mixed units: 1 m 25 cm = 100 cm + 25 cm = 125 cm; 3 km 400 m = 3 000 m + 400 m = 3 400 m.
Measure accurately
- Start at the 0 on the ruler, not at the edge.
- Read the smallest marks: each small mark is 1 mm.
Measure and convert
- Instruments: ruler, metre stick, tape measure, and a trundle wheel for long distances outside.
- Converting with fractions and decimals: ½ m = 50 cm; 3,05 m = 305 cm; 1,25 km = 1 250 m; 45 mm = 4,5 cm.
Length problems
First change all the lengths to the same unit before you add, subtract, multiply or divide.
- A rope is 5 m long. Thabo cuts off 3 pieces of 85 cm. How much is left? 3 × 85 cm = 255 cm = 2,55 m; 5 m − 2,55 m = 2,45 m.
- A plank of 2,4 m is sawn into 4 equal pieces: 240 cm ÷ 4 = 60 cm each.
- Sipho walks a 1,2 km route 3 times: 3 × 1,2 km = 3,6 km = 3 600 m.
Estimate first: 3 pieces of almost 1 m is almost 3 m, so a bit more than 2 m is left.
Reading a ruler and a tape measure
- On a ruler each small mark is 1 mm: 7 cm and 4 marks = 7,4 cm = 74 mm.
- On a tape measure you read metres and centimetres: 1 m and 35 cm = 1,35 m = 135 cm.
Remember this and test yourself
- 10 mm = 1 cm; 100 cm = 1 m; 1 000 m = 1 km.
- Make the units the same first.
- Big to small: multiply. Small to big: divide.
- Estimate first, then check your answer.
- Measure from the 0.
- Small mark on a ruler = 1 mm.
Write these points in your book. Read them again the night before the test.
Big to small? Multiply, because you get more little pieces.
Important words
First say the answer yourself, then turn the card over.
Match column A to column B
Tap a word in column A, then its meaning in column B. You can also start in column B.
True or false?
Read the question and the answer. Is the answer right? Tap True or False.
Now the real quiz!
The quiz has many more questions on this topic. Every question shows straight away whether you are right and explains why.
Take the quiz: Length: rulers, tape measures and problems- Let your child work the examples on paper and explain them to you.
- The ticks (“I know this”) are saved on this device only. We never ask for names or emails.
Follows CAPS for Grade 6 Mathematics. Always check your teacher’s notes and textbook too.