Primary 3 · Measurement & Geometry
P3 length, mass and volume
In P3, your child measures long distances in kilometres and small amounts of liquid in millilitres. They write measurements in two units at once, like 3 kg 200 g, and convert between the two. The number that matters is 1000.
- Taught in
- Term 3
- Syllabus
- 2 skills
- Usual slip
- Using 100, not 1000
What your child learns in P3 length, mass and volume
Two skills, each with what it looks like on a worksheet.
See the syllabus wording
- measuring: length in kilometres (km), volume of liquid in millilitres (ml)
- measuring length/mass/volume (of liquid) in compound units
- converting a measurement in compound units to the smaller unit, and vice versa: kilometres and metres, metres and centimetres, kilograms and grams, litres and millilitres
Kilometres and millilitres
Two new units in P3: the kilometre for long distances, and the millilitre for small amounts of liquid. 1 km is 1000 m, and 1 ℓ is 1000 mℓ.
| Point | Value |
|---|---|
| 0 | 0 |
| 250 m | 250 |
| 500 m | 500 |
| 750 m | 750 |
| 1000 m | 1000 |
| Reading | mℓ |
|---|---|
| Level | 1000 |
Two units at once, both ways
A measurement can use two units, such as 2 km 480 m. In metres, 2 km is 2000 m, so it is 2480 m. To go back, split at the thousands. Metres and centimetres split at the hundreds.
| Bigger unit | Smaller unit |
|---|---|
| 1 km | 1000 m |
| 1 m | 100 cm |
| 1 kg | 1000 g |
| 1 ℓ | 1000 mℓ |
Key facts and formulas
- Length1 m = 100 cm. Read the metres, then the centimetres.
Object Left (cm) Right (cm) 1 m 35 cm 0 135 - Mass1 kg = 1000 g. Read the kilograms, then count the small marks: each is 100 g.
Figure Reading bag on a kitchen scale read the mass off the scale - Volume of liquid1 ℓ = 1000 mℓ. Read the scale where the water is level.
Reading mℓ Level 1250 - Changing unitsTo one unit: change the bigger unit, then add. To two units: take out the thousands.
In two units In one unit 2 km 480 m 2480 m 5 m 8 cm 508 cm 2 kg 75 g 2075 g 1 ℓ 50 mℓ 1050 mℓ
Words to know
- Convert
- Write the same measurement in a different unit.
- Compound units
- A measurement in two units at once, such as 2 km 480 m.
- Kilometre (km)
- A long distance. 1 km is 1000 m.
- Millilitre (mℓ)
- A small amount of liquid. 1 ℓ is 1000 mℓ.
- Smaller unit
- The smaller the unit, the bigger the number. 3 km is 3000 m.
The sentence that costs the mark
A road is 3 km long. How long is it in metres?
What the working usually does
× 1003 km=300 m
Uses 100, as if kilometres worked like metres and centimetres. The answer is ten times too small.
What the question asked
× 10003 km=3000 m
1 km is 1000 m, so 3 km is 3 lots of 1000 m.
300 is a tidy number, so it slips past. Two checks catch it: the factor (1 km is 1000 m), and the size. A 3 km road is a long walk, so it must be thousands of metres.
The same P3 length, mass and volume question, worked properly
Lah works through it the way she does every question in StudyLah: one step at a time, marking the picture as she goes.
Write 4025 m as kilometres and metres.
- We want kilometres and metres. 1 km is 1000 m, not 100 m.
- Splitting 4025 at the hundreds gives 40 km 25 m. That uses 100, which is for metres and centimetres.
- Split at the thousands instead: 4025 m = 4000 m + 25 m. And 4000 m is 4 km.
- So 4025 m is 4 km 25 m.
Every question in StudyLah comes with a walkthrough like this one.
Try it freeThree quick P3 length, mass and volume questions
Try them together, then tap to check.
Question 1
Devi wanted to cycle 3 km 150 m. She has cycled 4 laps of a park, and each lap is 600 m. How much further must Devi cycle?
Show answer
Answer750 m. 3 km 150 m is 3150 m. 4 laps are 4 × 600 = 2400 m, and 3150 − 2400 = 750.
Question 2
Wei Ming cycled 950 m from his flat to the park, then to the pool. The second path is 150 m longer. Find the total distance in kilometres and metres.
| Leg | Distance |
|---|---|
| Flat → Park | 950 m |
| Park → Pool | ? |
Show answer
Answer2 km 50 m. Park to pool is 950 + 150 = 1100 m. The total is 950 + 1100 = 2050 m, which is 2 km 50 m.
Question 3
Daniel walks along the route shown. How far is the clinic from the playground?
| Leg | Distance |
|---|---|
| Flat → Playground | 550 m |
| Playground → Shop | 1650 m |
| Shop → Clinic | 350 m |
Show answer
Answer2000 m. 1650 + 350 = 2000 m, which is 2 km. The 550 m from the flat is not needed.
Helping at home
How to tell it has clicked
Ask two conversions, one each way: how many metres in 2 km, and how many kilometres and metres in 5030 m. A child who says 2000 m and 5 km 30 m has the factor and the zeros. 200 m or 5 km 300 m means not yet.
Before your child works, ask: will the number get bigger or smaller? Going to a smaller unit, it always gets bigger.
Try this tonight
A 1-litre bottle holds 1000 mℓ, and a teaspoon holds about 5 mℓ. It would take 200 teaspoons to fill the bottle. The small unit piles up into a big number.
On a walk, read a signboard that says 1 km and ask how many metres that is. Then guess how many big steps it would take.
Before and after P3 length, mass and volume
Builds on
Primary 2 LengthMeasures and compares lengths in m and cm
Builds on
Primary 2 MassChooses grams or kilograms by feel
Builds on
Primary 2 VolumeMeasures and compares liquid in litres
You are here
Primary 3 Length, Mass and Volume
Converts km, m, kg, g, ℓ and mℓ
Leads to
Primary 5 Volume of Cube and CuboidBuilds cuboids from unit cubes
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See how your child is doing on this topic
StudyLah marks each step separately, so you can see whether it was the setup or the arithmetic that cost the mark.