Length: Estimate and Measure with a Ruler in Centimetres

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1 Getting Started
2 Watch and Notice
3 Try It Together
4 Class Challenge
5 Write Your Estimates in Your Copy
6 What Did We Notice?
7 What's Next
Pupil practice

1 - Getting Started ~4 mins

Illustration for Getting Started Look at this new pencil held against a ruler. Roughly how long do you think it is? Is it more or less than ten centimetres? Hold up a hand if you think more, and a hand if you think less.

Teacher Notes

Take three hands-up estimates, not open call-outs. Don't reveal the actual length yet — the lesson is about estimating first, then checking. More or less than ten? is enough to get every pupil committing to a guess.

👇 Mark your steps as done as you complete them.

+5 XP

2 - Watch and Notice ~8 mins

Watch four objects being measured on the ruler. Each time, notice where the object starts and which mark its far end reaches. Why do we always begin at zero?

Teacher Notes

Point to the start of each object first: it sits on zero, not on 1. If we began at 1 we would miss the first centimetre and read one short, because there is no length yet at zero.

Crayon: zero end first, then trace to 6. It is 6 cm.

Pencil: ask the class to read the far mark before you confirm. Reaches 9, so 9 cm.

Copybook edge: emphasise reading past the 10 — ten, then one more. Stops at 11, so 11 cm.

Rubber: a short one, showing the same rule holds for small objects. Far edge on 4, so 4 cm.

👇 Mark your steps as done as you complete them.

+10 XP

3 - Try It Together ~11 mins

Let's read the length of the object on the ruler together. Before anyone reads the far mark, we'll check the zero is lined up with one end. One pupil at a time will come up and read the object on the board to the nearest centimetre; everyone else watches the board and gets ready to say whether they agree.

Read the object to the nearest centimetre

Teacher Notes

This round is for talking it through together — a pupil reads at the board and the rest of the class agrees or corrects out loud.

Call up an individual pupil to read the object currently on the board to the nearest centimetre. Before they read, ask the class: is the zero lined up? If a pupil reads from the 1, that is the teaching moment — the measurement comes out one centimetre short. After each pupil, change the object on the board to a new length (use the interactive controls) so the next pupil reads a fresh length. Rotate four pupils across four resets.

+15 XP

4 - Class Challenge ~9 mins

Before you measure at your desks, watch one worked example of measuring to the nearest centimetre when the end does not land on a mark.

A glue stick is lined up with zero. Its far end sits between 7 and 8, a little closer to 8. The nearer centimetre is 8, so we record 8 cm.

Now measure five real objects on your own desk with your own ruler. Work through it in three clear steps:

First, estimate all five in your head: your rubber, your glue stick, the short side of your copybook, your pencil, and one object from the front desk that looks close to 10 cm.
Then measure all five, one at a time, to the nearest centimetre. Line the zero up with one end every time. If the far end sits between two marks, choose the nearer centimetre (halfway or past, round up).
Last, put your five lengths in order, shortest first.

Tip

If five feels like a lot, just do the first three objects, your rubber, your glue stick and your pencil, and order those.

Hands-on Task

Teacher Notes

Teach nearest centimetre once, on the board, before anyone measures at desks. Hold a real glue stick (or similar) on a class ruler: zero lined up, far end between 7 and 8, clearly nearer 8. Say and write: nearer mark is 8, so 8 cm. If it looks dead halfway, round up to 8.

Then send pupils to the desk task. Circulate and catch the make-or-break slip: starting from 1 instead of 0 (reading one centimetre short). Also watch for pupils always reading down to the lower mark instead of choosing the nearer one.

Keep a small shared bank of about-10 cm objects on the front desk. Fast finishers find which two of their objects differ by the most centimetres, and by how many.

+15 XP

5 - Write Your Estimates in Your Copy ~3 mins

COPYBOOK MOMENT

In your maths copy, write each object you just measured — your rubber, your glue stick, the short side of your copybook, your pencil and your near-10-cm object — with your estimate first, then its measured length in centimetres beside it. Put a star beside any estimate that was within 1 cm of the real length.

Teacher Notes

Walk the room glancing at the estimate-then-measure layout — this is whole-class copybook practice, not marking. Pupils have just measured these objects, so the column has defined entries. Praise close estimates to build the habit of estimating before measuring.

+10 XP

6 - What Did We Notice? ~3 mins

MATHS TALK

Why do we line the zero up with the end of an object, and not the number 1?

Teacher Notes

Listen for pupils explaining that the zero is the true start — there is no length yet at zero. Revoice a strong answer: so if we start at the 1, we miss the first centimetre and our measurement comes out short. Head off the idea that you can start anywhere as long as you count the marks.

+10 XP

7 - What's Next ~2 mins

Today you learned to:

Estimate a length first, then measure it to the nearest centimetre.
Line the zero up with one end and read the centimetre mark at the other end.

Coming up

Next we look more closely at the tiny marks between the centimetres, called millimetres, so we can measure even more carefully.

Teacher Notes

Keep this brisk. The natural next step is the centimetres-and-millimetres lesson — flag that the ruler has smaller marks the class will use next.

+5 XP

Pupil practice

Module 4 · Measures: Length, Weight and Capacity Measures

Lesson 43 · Length: Estimate and Measure with a Ruler in Centimetres

Download Activity Book page (PDF)

End of lesson

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This lesson is copyright of Coding Ireland 2017 - 2025. Unauthorised use, copying or distribution is not allowed.

Teacher Class Feed

1 - Getting Started ~4 mins

2 - Watch and Notice ~8 mins

3 - Try It Together ~11 mins

Read the object to the nearest centimetre

4 - Class Challenge ~9 mins

Hands-on Task

5 - Write Your Estimates in Your Copy ~3 mins

6 - What Did We Notice? ~3 mins

7 - What's Next ~2 mins

Today you learned to:

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