Measuring Length, Mass and Capacity
What this lesson covers
- Length is how long, mass is how heavy, capacity is how much it holds.
- Units must all be the same size, with no gaps or overlaps.
- Centimetres, grams and millilitres are the same for everyone.
- Rulers, scales and jugs are marked in these units.
Three things we measure
- Length: how long or tall something is.
- Mass: how heavy something is.
- Capacity: how much something holds.
| Measure | Question | Unit |
|---|---|---|
| length | How long? | centimetres (cm) |
| mass | How heavy? | grams (g) |
| capacity | How much does it hold? | millilitres (mL) |
Try it: length, mass or capacity?
Measure with things you have
- You can measure with paper clips, blocks or cups.
- Use units that are all the same size.
- Put them end to end, with no gaps and no overlaps.
- Guess first, then measure, and see how close you were.
| To measure | Use | Result |
|---|---|---|
| a desk's length | paper clips in a line | 12 paper clips |
| a book's mass | blocks on a balance | 9 blocks |
| a jug's capacity | cups of water | 5 cups |
Compare and order
- Measure each thing with the same unit, then compare the numbers.
- Shortest to longest: crayon, pencil, ruler.
| Object | Length in paper clips |
|---|---|
| pencil | 6 |
| ruler | 10 |
| crayon | 3 |
Why we use cm, g and mL
- Your hand span and a grown-up's hand span are different sizes.
- A centimetre is the same size for everyone, everywhere.
- So if you say a book is 20 cm long, a friend knows exactly how long.
Read the tool
- A ruler: line the end of the object up with 0, then read the number at the other end.
- Kitchen scales: put the thing on and read the grams.
- A measuring jug: fill it and read the mark at the top of the water.
| Tool | Measures | Example |
|---|---|---|
| ruler | length in cm | a crayon is 8 cm |
| kitchen scales | mass in g | an apple is 150 g |
| measuring jug | capacity in mL | a glass of milk is 250 mL |
Try it: which tool would you use?
Estimate first
- Use something you know to make a good guess.
- Your finger is about 1 cm wide.
- A small paper clip is about 1 g.
- A teaspoon holds 5 mL.
Common mistakes
- Leaving gaps between the paper clips.Line the units up end to end, with no gaps or overlaps, or the count will be wrong.
- Starting the ruler at the 1.Line the end of the object up with 0.
- Mixing big and small blocks when measuring.Use units that are all the same size.
Your turn
1
Which unit tells how much a cup holds: cm, g or mL?
2
A pencil is 7 paper clips long. A crayon is 4 paper clips long. Which is longer?
3
Order shortest to longest: ruler 30 cm, shoe 18 cm, pencil 12 cm.
4
Kitchen scales show 500 g for a bag of rice. What is its mass?
5
Why is cm better than hand spans for telling a friend how long something is?
Show answer
1. mL 2. the pencil 3. pencil, shoe, ruler 4. 500 g 5. A cm is the same for everyone; hand spans are different sizes.
What to take away
- Length, mass and capacity are different things to measure.
- Same-size units, no gaps, no overlaps.
- cm, g and mL mean the same to everyone.
- Start a ruler at 0.
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