Capacity

CBC Grade 5 Mathematics — Capacity

Lesson Objectives

By the end of this topic, a learner should be able to:

• Identify the millilitre as a unit for measuring capacity
• Explain the relationship between litres and millilitres
• Convert between litres and millilitres
• Add, subtract, multiply, and divide capacities given in litres and millilitres
• Appreciate the use of litres and millilitres in everyday situations

Capacity

Capacity is how much a container holds. You already know the litre. Grade 5 adds the millilitre, for small amounts.

a) The millilitre

A millilitre is a very small amount of liquid. The short way to write it is ml.

A teaspoon holds about 5 ml. A medicine spoon holds 5 ml too.

1 litre = 1 000 millilitres.

b) Everyday amounts

Container	About
Teaspoon	5 ml
Cup	250 ml
Small water bottle	500 ml
Milk packet	1 litre
Jerrican	20 litres

Knowing a few of these helps you judge whether an answer is sensible.

c) Converting

To change litres to millilitres, multiply by 1 000.

To change millilitres to litres, divide by 1 000.

A check: millilitres are smaller, so there are more of them. Litres give the smaller number.

d) Adding and subtracting

Add the millilitres first, then the litres.

The millilitres may come to 1 000 or more. Change each 1 000 into a litre and carry it over.

In subtraction there may not be enough millilitres. Borrow one litre and turn it into 1 000 ml.

e) Multiplying and dividing

Multiply or divide each part, then tidy up.

Three bottles of 1 l 500 ml hold 3 l 1 500 ml. Change the 1 500 ml, giving 4 l 500 ml.

A 6-litre container shared into 4 equal parts gives 1 l 500 ml each.

f) Reading a measuring jug

Stand the jug on a flat table. Do not hold it in your hand.

Bend down so your eyes are level with the liquid.

Read the mark where the surface sits. Looking from above or below gives the wrong answer.

g) Where this is used

Buying milk or cooking oil. Measuring medicine for a child. Filling a jerrican at the tap. Following a recipe.

:::checkpoint Check yourself

1. How many millilitres make one litre?
2. Change 3 litres into millilitres.
3. Change 4 200 ml into litres and millilitres.
4. Add 2 l 800 ml and 1 l 400 ml. :::

Definitions

• Litre (L) — a unit of capacity equal to 1,000 millilitres.
• Millilitre (ml) — the base unit of capacity.

Must Remember

1. 1 L = 1,000 ml.
2. Convert mixed L/ml amounts to ml before calculating.
3. Convert the final answer back to L and ml if needed.
4. Multiply to convert L to ml; divide to convert ml to L.

Conclusion

Convert to millilitres first, calculate, then convert back — same pattern as Length.