Volume & Capacity — Grade 3 Mathematics
In Grade 3, we build on our understanding of capacity by working confidently with millilitres (ml) and litres (L), reading scale intervals on measuring jugs, and solving multi-step capacity problems involving all four operations.
Key Facts
1 litre (L) = 1 000 millilitres (ml)
Converting:
L → ml: multiply by 1 000 (e.g., 2.5 L = 2 500 ml)
ml → L: divide by 1 000 (e.g., 750 ml = 0.75 L)
Capacity = how much a container can hold (maximum).
Volume = how much liquid is actually inside it.
Converting:
L → ml: multiply by 1 000 (e.g., 2.5 L = 2 500 ml)
ml → L: divide by 1 000 (e.g., 750 ml = 0.75 L)
Capacity = how much a container can hold (maximum).
Volume = how much liquid is actually inside it.
Reading Measuring Jugs
750 ml
500 ml
250 ml
700 ml
1 500 ml
1 000 ml
500 ml
800 ml
💡 Reading scales: Find the two labelled marks the liquid is between. Divide the gap by the number of intervals to get each small division's value.
Worked Examples
Example 1 — Converting Units
Convert: (a) 3.25 L to ml (b) 1 800 ml to L
- (a) 3.25 × 1 000 = 3 250 ml
- (b) 1 800 ÷ 1 000 = 1.8 L
Example 2 — Adding Capacities
A recipe uses 350 ml of milk and 1.2 L of water. What is the total liquid in ml?
- Convert 1.2 L = 1 200 ml
- Total = 350 + 1 200 = 1 550 ml
Example 3 — Real World: Sharing Juice 🧃
A 2 L bottle of juice is shared equally among 8 children. How much does each child get in ml?
- 2 L = 2 000 ml
- 2 000 ÷ 8 = 250 ml per child
Practice Questions
1. Convert 4.5 L to millilitres.
✅ 4.5 × 1 000 = 4 500 ml
2. Convert 2 750 ml to litres.
✅ 2 750 ÷ 1 000 = 2.75 L
3. A fish tank holds 15 L. It currently has 9 500 ml in it. How much more water is needed to fill it?
✅ 15 L = 15 000 ml; 15 000 − 9 500 = 5 500 ml = 5.5 L
4. Three bottles contain 650 ml, 1.3 L, and 850 ml. What is the total in L?
✅ 650 + 1 300 + 850 = 2 800 ml = 2.8 L
5. Which is more: 1.5 L or 1 400 ml?
✅ 1.5 L = 1 500 ml; 1 500 > 1 400 → 1.5 L is more
Key Points to Remember
- 1 L = 1 000 ml — the key conversion fact.
- L → ml: multiply by 1 000. ml → L: divide by 1 000.
- Always convert to the same unit before adding, subtracting, or comparing.
- Capacity = maximum the container holds. Volume = what's actually inside.
- Read measuring jug scales carefully — identify the scale interval first.