Converting units
km, m, cm and mm; kg and g; ℓ and mℓ. Learn when to multiply and when to divide, and why the comma moves. Read one step, play with it, then tap “I understand this”.
The unit ladder
1 km = 1 000 m · 1 m = 100 cm · 1 cm = 10 mm · 1 kg = 1 000 g · 1 ℓ = 1 000 mℓ. The prefix tells you the number: kilo = 1 000, centi = a hundredth, milli = a thousandth.
The converting machine
Choose the units, the direction and a number. Watch how the digits move in the place value table.
When you multiply by 1 000, every digit becomes worth 1 000 times more. The 2 ones become 2 thousands, so it moves 3 places to the left. It looks as if the comma moves, but really the digits move.
Multiply or divide?
Think of money: R1 is 100 cents. When you change rands into cents, you get more pieces, because cents are smaller. It is the same with measurement:
Big unit → small unit: multiply. Small unit → big unit: divide.
- 2,5 kg → g: grams are smaller, so multiply: 2,5 × 1 000 = 2 500 g.
- 750 mℓ → ℓ: litres are bigger, so divide: 750 ÷ 1 000 = 0,75 ℓ.
- 4 m → cm: multiply by 100: 400 cm.
Check that your answer makes sense. A small unit must get a big number. 2 500 g and 2,5 kg are the same mass.
A smaller unit fits in more times. 1 kg has 1 000 g, so 2,5 kg is 2,5 × 1 000 = 2 500 g. More small pieces means a bigger number, but the mass stays the same.
Practise converting
Convert
Type the answer. Use the comma key for decimals.
Compare different units
Which is heavier: 1,2 kg or 1 050 g? You cannot compare 1,2 and 1 050. First make the units the same: 1,2 kg = 1 200 g, and 1 200 g is more than 1 050 g.
Which is more?
Choose the biggest amount.
Correct: 01,2 and 1 050 are numbers in different units, like rands and cents. You cannot compare R2 and 150c by just looking at 2 and 150. Only when both are in the same unit does the bigger number also mean the bigger amount.
Word problems with units
In a word problem the units are often mixed. First change everything to one unit, and then calculate.
Step by step
Try it yourself first. Then tap to see the steps one by one.
1,5 ℓ + 250 mℓ is not 251,5! First 1,5 ℓ = 1 500 mℓ, then 1 500 + 250 = 1 750 mℓ.
Check yourself
- 1 km = 1 000 m, 1 m = 100 cm, 1 cm = 10 mm, 1 kg = 1 000 g, 1 ℓ = 1 000 mℓ.
- Big → small unit: multiply. Small → big unit: divide.
- × 1 000 moves every digit 3 places left: 2,5 kg = 2 500 g.
- Make the units the same before you compare or calculate.
Write these points in your maths book. Read them again the night before the test.
Quick questions
Tap an answer. If you get one wrong, read why and go back to that step. You get new questions every time.
You ticked all 5 steps! Now you are ready for the quiz.- Practice sheet for this classQuestions + memo · 2 A4 pagesPractice sheet
- Measurement9 pages · PDFPaperMemo
Ready for more? The Grade 5 converting units quiz gives you new questions every time.
- One step a day is enough. Ten calm minutes work better than an hour the night before the test.
- Look at packets in the kitchen together: “The sugar is 2,5 kg. How many grams is that?” “The bottle is 750 mℓ. Is that more or less than a litre?”
- Ask your child to tell you the rule in their own words. If they can explain it, they understand it.
- The ticks (“I understand this”) are saved on this device only. We never ask for names or emails.
Follows CAPS for Grade 5 Maths. Always check your teacher’s notes and textbook too.