Length — Grade 1 Mathematics

Length tells us how long or how tall something is. We measure length every day — checking if a shelf is wide enough, seeing how tall we have grown, or finding out which pencil is longer. Learning to measure length accurately is an essential life skill!

Key Words for Length

Long / Short — used to describe and compare lengths.
Tall / Short — used for height (vertical measurement).
Longer than / Shorter than — comparing two objects.
Centimetre (cm) — the standard unit of length for small objects.
Metre (m) — the standard unit for longer lengths. 1 m = 100 cm.

💡 Tip: Always start measuring from the zero end of the ruler, not the edge of the ruler!

Non-Standard vs Standard Units

Before rulers existed, people measured with body parts or objects around them. These are called non-standard units.

Examples: counting paper clips 📎, hand spans, or footsteps.

The problem? A child's hand is smaller than an adult's hand — so results differ! That is why we use standard units (cm, m) that are the same for everyone.

Worked Examples

Example 1 — Comparing with Words

Look at two pencils. Pencil A is 12 cm long. Pencil B is 8 cm long. Which is longer?

Pencil A

12 cm

Pencil B

8 cm

12 cm > 8 cm → Pencil A is longer.

Example 2 — Reading a Ruler

A worm 🪱 is placed on a ruler from 0 cm to 6 cm. How long is the worm?

012345678910

🪱

The worm is 6 cm long.

Example 3 — Real World Scenario

Sam measures his bedroom with footsteps. It takes 12 footsteps. His sister counts 15 footsteps. Why are the numbers different?

Sam has bigger feet → fewer steps needed. This shows why non-standard units are unreliable — always use a ruler or tape measure!

Practice Questions

1. Pencil A = 9 cm, Pencil B = 14 cm. Which is shorter?

✅ Pencil A (9 cm) is shorter than Pencil B (14 cm).

2. How many centimetres are in 1 metre?

✅ 1 metre = 100 centimetres

3. A ribbon starts at 0 cm and ends at 13 cm on a ruler. How long is the ribbon?

✅ The ribbon is 13 cm long.

4. Arrange from shortest to longest: 5 cm, 11 cm, 2 cm, 8 cm

✅ 2 cm, 5 cm, 8 cm, 11 cm

5. Is measuring a desk in "pencil lengths" a standard or non-standard method?

✅ Non-standard — pencils come in different sizes, so results will vary.

Key Points to Remember

Length tells us how long or tall something is.
Standard units: centimetres (cm) and metres (m).
1 metre = 100 centimetres.
Always measure from the zero mark on the ruler.
Use standard units so everyone gets the same answer.

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