Primary 6 Foundation maths · Measurement & time · About 12 minutes
Find liquid volume in rectangular tanks
Mark the water surface first, then use that depth with the base.
Start the interactive lesson →Open practice activity
What you will learn
- Find liquid volume in rectangular tanks
Models used: number sentences, stories, tables.
Before you start
Count a layer, then stack the layers
One layer is 4 cubes wide and 3 cubes deep. It contains 12 cubes.
Count cubes across a layer, then count the layers. Some cubes are hidden.
One layer is 4 cubes wide and 3 cubes deep. It contains 12 cubes.
A tank 10 cm tall with water 3 cm deep holds base area × 3. The empty space above holds no water.
Width 4, height 1, depth 3
Count cubes across a layer, then count the layers. Some cubes are hidden.
Stack a second matching layer. Now there are two lots of 12 cubes.
Width 4, height 2, depth 3
Count cubes across a layer, then count the layers. Some cubes are hidden.
A third layer gives 36 cubes. Remember the cubes hidden inside.
12 + 12 + 12 = 36
Width 4, height 3, depth 3
What did the picture help us see?
A third layer gives 36 cubes. Remember the cubes hidden inside.
Worked example: A new example, together
A rectangular tank has a 4 cm by 5 cm base and water depth 4 cm. Find the water volume.
| Width | Depth | Height / layers |
|---|---|---|
| 4 | 5 | 4 |
All dimensions refer to the same unit. Read each value with the heading above its column.
Mark the water surface first, then use that depth with the base.
Equal layers connect base area and height with total volume.
All dimensions refer to the same unit Width Depth Height / layers 4 5 4 All dimensions refer to the same unit. Read each value with the heading above its column.
One layer contains 4 × 5 = 20 unit cubes.
All dimensions refer to the same unit Width Depth Height / layers 4 5 4 A rectangular tank has a 4 cm by 5 cm base and water depth 4 cm. Find the water volume.
80 cm³
All dimensions refer to the same unit. Read each value with the heading above its column.
One layer contains 4 × 5 = 20 unit cubes.
All dimensions refer to the same unit Width Depth Height / layers 4 5 4 All dimensions refer to the same unit. Read each value with the heading above its column.
There are 4 equal layers.
All dimensions refer to the same unit Width Depth Height / layers 4 5 4 All dimensions refer to the same unit. Read each value with the heading above its column.
Count all layers: 20 × 4 = 80.
All dimensions refer to the same unit Width Depth Height / layers 4 5 4 All dimensions refer to the same unit. Read each value with the heading above its column.
Check the result against the question we started with.
20 × 4 = 80.
We found 80 cm³. Equal layers connect base area and height with total volume.
All dimensions refer to the same unit Width Depth Height / layers 4 5 4
Common mistakes to discuss
- Using the tank’s height. The water’s depth gives its volume, not the height of the container.
Check your understanding
- Find liquid volume in rectangular tanks
- find a liquid volume from the base and the water depth
- check the answer against the original quantities and units
Explain your reasoning to an adult, then try a fresh question in the interactive lesson. A result from one attempt is not proof of lasting mastery.
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