P3 Measurement: Length, Mass and Volume

The red marker on a scale tells a story only when you read its labels. A route marker at 3 km is not 3 m, and 1 l 250 ml is not 1250 l. Keep the unit beside every number and the amount stays clear.

Parents: let your child point to each graduation and predict the reading before revealing the conversion. Ask them to say the unit aloud each time.

By the end you will be able to read a simple scale, write compound measurements, and convert all four P3 unit pairs in either direction.

Read a graduated scale

A graduated scale gives you a number and a unit. Find the target, then count its minor graduations from a labelled mark. A route scale labelled 0, 1, 2, 3, 4 and 5 km with its marker at 3 says 3 km. A jug labelled 0, 250, 500, 750 and 1000 ml with its meniscus at 750 says 750 ml.

Read the small graduations on a ruler or balance in the same way. For example, a ruler ending at 235 cm gives 200 cm and 35 cm, which is 2 m 35 cm. A balance can show 3 kg 125 g, and a jug can show 1 l 250 ml. The two parts belong to different unit columns.

Four unit links

The four P3 conversion links are:

Going from a larger unit to its smaller partner makes the number larger, so multiply by the link. Going from the smaller unit to the larger partner makes the number smaller, so divide by the link. P3 examples here use whole numbers and compound remainders.

Conversion lab: the amount does not change

Try each pair. The lab shows actual graduated instruments and lets you switch between a compound reading and one smaller unit. The red target, the factor label and the result text should agree.

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Measurement lab: same amount, two readings

🤔 Predict first: 2 km 350 m is how many metres?

2,035 m2,350 m23,500 m

For example, the two directions for kilometres and metres are:

Kilometres and metres

$$2\times1,000+350=2,350\,\text{ m}$$

$$2,350\,\text{ m}=2\,\text{ km }350\,\text{ m}$$

The same structure works for the other pairs:

All four links

$$4\times100+6=406\,\text{ cm}$$

$$3\times1,000+125=3,125\,\text{ g}$$

$$1\times1,000+250=1,250\,\text{ ml}$$

Three graduated practice checks

Try each complete question first. Open the solution only after writing a number and its unit.

Practice 1 — read the instruments

A route marker is on 3 km. A jug meniscus is on 750 ml. What are the two readings?

Show the worked reading

Read the targets

$$3\,\text{ km}$$

$$750\,\text{ ml}$$

The two readings are 3 km and 750 ml.

Practice 2 — convert to smaller units

Convert 4 m 6 cm to centimetres and 3 kg 125 g to grams.

Show the worked conversion

Convert the larger part first

$$4\times100+6=406\,\text{ cm}$$

$$3\times1,000+125=3,125\,\text{ g}$$

The answers are 406 cm and 3,125 g.

Practice 3 — convert back to compound units

Write 2,350 m and 1,250 ml as compound measurements.

Show the worked conversion

Split into the large and leftover parts

$$2,350=2\times1,000+350\Rightarrow2\,\text{ km }350\,\text{ m}$$

$$1,250=1\times1,000+250\Rightarrow1\,\text{ l }250\,\text{ ml}$$

The answers are 2 km 350 m and 1 l 250 ml.

Watch out — these are easily mixed up

Quick recap

🎯 Mastery check

Answer all 8 — your progress is saved on this device.

1. A route marker is exactly at the 3 km graduation. What is the route length?

   3 m30 km3 km

2. A jug meniscus is at the 750 ml graduation. What is the volume?

   75 ml750 ml750 l

3. Write 2 km 350 m in metres.

   2,035 m2,350 m23,500 m

4. Write 406 cm as metres and centimetres.

   4 m 6 cm40 m 6 cm4 m 60 cm

5. Write 3 kg 125 g in grams.

   3,125 g3,0125 g312.5 g

6. Write 1,250 ml as litres and millilitres.

   1 l 25 ml1 l 250 ml12 l 50 ml

7. A balance reads 3 kg 125 g. Which statement keeps the same mass?

   3,125 g312.5 g31,250 g

8. Which conversion uses division?

   4 l to ml2 km to m2,350 m to km and m

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