Choose units for capacity & volume
Theory
Choose the unit that gives a tidy number: millilitres for small amounts, litres for everyday containers, kilolitres for very large ones. Each step between them is \(\times 1000\).
Capacity is how much a container can hold. Volume is how much space a solid takes up.
Small amounts use millilitres (mL), everyday containers use litres (L), and very large amounts use kilolitres (kL). Solid shapes use cubic units, \(\text{cm}^3\) or \(\text{m}^3\).
Each step is a thousand: \(1\text{ L} = 1000\text{ mL}\) and \(1\text{ kL} = 1000\text{ L}\). Volume and capacity meet here, because \(1\,\text{cm}^3\) of space holds exactly \(1\) mL, and \(1\,\text{m}^3\) holds \(1000\) L.
Use the size of the object to choose the unit.
| Unit | Good for | Rough size |
|---|---|---|
| mL | teaspoon, medicine dose | teaspoon ≈ \(5\) mL |
| L | drink bottle, bucket, bathtub | bucket ≈ \(10\) L |
| kL | pool, rainwater tank | tank ≈ \(10\) kL |
| \(\text{cm}^3\) | small solid, small box | \(1\,\text{cm}^3 = 1\) mL |
| \(\text{m}^3\) | room, shipping container | \(1\,\text{m}^3 = 1000\) L |
Choosing a unit and converting
- Estimate the size of the amount and pick the unit that gives a number that is easy to say.
- To a smaller unit (L to mL, kL to L), multiply by \(1000\); the number grows.
- To a larger unit (mL to L, L to kL), divide by \(1000\); the number shrinks.
- Between volume and capacity, use \(1\,\text{cm}^3 = 1\) mL and \(1\,\text{m}^3 = 1000\) L.
A teaspoon holds about \(5\) mL, a very small amount.
The sensible unit is millilitres.
A millilitre is smaller, so multiply.
| \(3 \times 1000\) | \(=\) | \(3000\) |
So \(3\text{ L} = 3000\) mL.
The units are the same size.
| \(250\,\text{cm}^3\) | \(=\) | \(250\text{ mL}\) |
The capacity is \(250\) mL.
A litre is larger, so divide.
| \(3500 \div 1000\) | \(=\) | \(3.5\) |
So \(3500\text{ mL} = 3.5\) L.
Common pitfalls
Frequently asked questions
What is the difference between capacity and volume?
Capacity is how much a container can hold; volume is how much space a solid takes up. They use related units because \(1\,\text{cm}^3\) of space holds exactly \(1\) mL.
Which unit should I use for a drink bottle?
Litres. A large drink bottle holds about \(1\) to \(2\) L, which is a tidy number. In millilitres that would be \(1000\) to \(2000\) mL.
How do I change litres to millilitres?
Multiply by \(1000\), because a millilitre is smaller and it takes more of them. For example \(3\text{ L} = 3 \times 1000 = 3000\) mL.
How many litres fit in one cubic metre?
\(1000\) L. A cube one metre along every edge holds \(1000\) L of water, which is also \(1\) kL.
Is a millilitre the same as a cubic centimetre?
Yes. \(1\) mL of water fills exactly \(1\,\text{cm}^3\) of space, so the two measure the same amount.