Primary 3 Length, Mass and Volume
Keywords
- Compound units
- A measurement written using both large and small units, such as 3 km 250 m.
- Kilometre
- 1 km = 1 000 m.
- Metre
- 1 m = 100 cm.
- Kilogram
- 1 kg = 1 000 g.
- Litre
- 1 ℓ = 1 000 mℓ.
Kilometres and metres
1 km = 1 000 m. To write km and m as metres, change the kilometres to metres and add the extra metres. To go back, make as many complete groups of 1 000 m as you can; the rest stays in metres.
1 km = 1 000 m
Change the large part to m first.
See worked example
Write 3 km 250 m in metres.
- 3 km = 3 × 1 000 m = 3 000 m.
- Add the extra 250 m: 3 000 m + 250 m = 3 250 m.
Answer: 3 250 m
Try together
Write 4 680 m in km and m.
Reveal the answer
4 680 m = 4 000 m + 680 m = 4 km 680 m.
Metres and centimetres
1 m = 100 cm. Change the metres to centimetres and add any extra centimetres. To change centimetres to m and cm, group them in hundreds. The leftover centimetres must be less than 100.
1 m = 100 cm
Change the large part to cm first.
See worked example
Write 5 m 36 cm in centimetres.
- 5 m = 5 × 100 cm = 500 cm.
- Add 36 cm: 500 cm + 36 cm = 536 cm.
Answer: 536 cm
Try together
Write 724 cm in m and cm.
Reveal the answer
724 cm = 700 cm + 24 cm = 7 m 24 cm.
Kilograms and grams
1 kg = 1 000 g. Change the kilograms to grams and add the extra grams. To change grams to kg and g, group them in thousands; the grams left over must be less than 1 000.
1 kg = 1 000 g
Change the large part to g first.
See worked example
Write 2 kg 350 g in grams.
- 2 kg = 2 × 1 000 g = 2 000 g.
- Add 350 g: 2 000 g + 350 g = 2 350 g.
Answer: 2 350 g
Try together
Write 4 075 g in kg and g.
Reveal the answer
4 075 g = 4 000 g + 75 g = 4 kg 75 g.
Litres and millilitres
1 ℓ = 1 000 mℓ. Change the litres to millilitres and add the extra millilitres. To change millilitres to ℓ and mℓ, group them in thousands; any amount left stays in millilitres.
1 ℓ = 1 000 mℓ
Change the large part to mℓ first.
See worked example
Write 3 ℓ 250 mℓ in millilitres.
- 3 ℓ = 3 × 1 000 mℓ = 3 000 mℓ.
- Add 250 mℓ: 3 000 mℓ + 250 mℓ = 3 250 mℓ.
Answer: 3 250 mℓ
Try together
Write 2 006 mℓ in ℓ and mℓ.
Reveal the answer
2 006 mℓ = 2 000 mℓ + 6 mℓ = 2 ℓ 6 mℓ.