Mass and volume
When you weigh something you are measuring its mass. When you pour a liquid you are measuring its volume. Both use a ladder of tens, just like length.
Mass — what is in your shopping basket
| Unit | Short for | Roughly |
|---|---|---|
| gram | g | one paperclip ≈ 1 g |
| decagram | dag | a small biscuit ≈ 1 dag (10 g) |
| kilogram | kg | a bag of sugar ≈ 1 kg |
| tonne | t | a small car ≈ 1 t (1 000 kg) |
The main equalities to memorise:
- 1 kg = 1 000 g
- 1 kg = 100 dag
- 1 dag = 10 g
- 1 t = 1 000 kg
Worked examples
A watermelon weighs 4 kg. How many grams is that?
4 kg = 4 × 1 000 g = 4 000 g.
A bag of nuts weighs 250 g. How many kilograms is that?
250 ÷ 1 000 = 0.25 kg (a quarter of a kilogram).
Three lorries together carry 8 500 kg. How many tonnes is that?
8 500 ÷ 1 000 = 8.5 t.
Volume — pouring and measuring
| Unit | Short for | Roughly |
|---|---|---|
| millilitre | ml | one drop ≈ 1 ml |
| centilitre | cl | a teaspoon ≈ 1 cl (5 ml is half) |
| decilitre | dl | a small mug ≈ 2 dl |
| litre | l | a big bottle of water = 1 l |
The main equalities to memorise:
- 1 l = 1 000 ml
- 1 l = 10 dl
- 1 dl = 100 ml
Worked examples
A juice carton has 1.5 l. How many millilitres is that?
1.5 l = 1.5 × 1 000 ml = 1 500 ml.
A recipe needs 750 ml of milk. How many litres is that?
750 ÷ 1 000 = 0.75 l (three quarters of a litre).
You drink three glasses of 2 dl water. How much have you drunk in total, in litres?
3 × 2 dl = 6 dl. And 6 dl = 6 ÷ 10 l = 0.6 l.
The same rule again
Going from a big unit to a small unit, you multiply. From a small unit to a big unit, you divide.
⚠️ Watch the ladder steps. Going from g straight to kg skips dag, so you divide by 1 000 (not 100). Going from ml to l skips cl and dl, so you divide by 1 000 too.
What's next
- Length conversions — same ladder, different units
- Time conversions — the 60s ladder
- Back to the introduction