Volume (Capacity) • Topic 3 of 5

Unit Conversion

Converting between litres and millilitres is simply multiplying or dividing by 1000, and the only real mistake children (and candidates) make is dropping or adding a zero. To change litres into millilitres, multiply by 1000: 2 L = 2 x 1000 = 2000 mL, and 5 L = 5000 mL. A neat way to see it is to move the number three places, since 1000 has three zeros. To change millilitres into litres, divide by 1000: 4000 mL = 4 L, and 2500 mL = 2 L 500 mL (because 2500 = 2000 + 500). Mixed measures are written as a litre part and a millilitre part, for example 3 L 250 mL, which equals 3000 + 250 = 3250 mL. When adding or subtracting capacities, line up litres with litres and millilitres with millilitres, and remember the carry-over happens at 1000, not at 100: if the millilitres add up to 1000 or more, carry 1 litre. For instance, 1 L 600 mL + 1 L 700 mL gives 2 L 1300 mL, and since 1300 mL = 1 L 300 mL, the answer is 3 L 300 mL. For subtraction you may need to borrow 1 litre as 1000 mL. The conversions must always stay exact: 1 L is 1000 mL, never 100 mL, and confusing this with the metric step for length or weight is a common slip.

✅ Solved examples

1. Convert 3 litres into millilitres.
3 L = 3 x 1000 = 3000 mL. Multiply litres by 1000 to get millilitres.
2. Convert 4500 mL into litres and millilitres.
4500 mL = 4000 mL + 500 mL = 4 L 500 mL. Divide by 1000: every 1000 mL is 1 litre, leaving 500 mL.
3. Add: 1 L 750 mL + 2 L 500 mL.
Add millilitres: 750 + 500 = 1250 mL = 1 L 250 mL. Add litres: 1 + 2 = 3 L, plus the carried 1 L = 4 L. Total = 4 L 250 mL.
4. Subtract: 5 L 200 mL - 1 L 600 mL.
You cannot take 600 from 200, so borrow 1 L (1000 mL): 200 becomes 1200 mL and litres drop from 5 to 4. Now 1200 - 600 = 600 mL and 4 - 1 = 3 L. Answer = 3 L 600 mL.

✏️ Practice — try these, take hints as needed

1. How many millilitres are there in 6 litres?
Multiply by 1000.
Move three places.
6000 mL
2. Write 2 L 250 mL entirely in millilitres.
2 L = 2000 mL.
Add the 250 mL.
2250 mL
3. Add 900 mL + 600 mL and give the answer in litres and millilitres.
900 + 600 = 1500 mL.
1000 mL makes 1 litre.
1 L 500 mL
4. A jug holds 2 L. A glass of 250 mL is filled from it. How many such glasses can be filled?
2 L = 2000 mL.
Divide 2000 by 250.
8 glasses

📝 Topic test — 8 questions

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