Grade by Grade
E. Spatial Sense · Shapes, Maps and Measurement

Measuring and Drawing with a Ruler

E2.3 A1About 35 minutes
Learning goals
  • I can measure length in centimetres with a ruler, starting at 0.
  • I can measure correctly even if I start at a number other than 0.
  • I can draw a line of a given length in centimetres.
  • I can measure longer things in metres with a metre stick or measuring tape.

Words to know

ruler
A measuring tool marked in centimetres. Many school rulers are 30 cm long.
zero mark
The 0 line on a ruler where measuring starts. It is not always right at the edge of the ruler!
metre stick
A measuring tool that is exactly 1 metre (100 cm) long.
measuring tape
A long, bendy measuring tool that can measure many metres.

Your ruler is a tool

Carpenters, tailors and builders use measuring tools every day. Today you will learn to use a ruler like a pro!

A ruler is like many 1-cm units glued together in a row. Instead of laying down units one by one, you just read the number.

Measuring from 0

  1. Find the 0 mark on the ruler. (On many rulers, it is a little bit in from the edge.)
  2. Line up the 0 mark with one end of the object.
  3. Keep the ruler straight along the object.
  4. Look at the other end. Read the number there.
  5. Say the number and the unit: "7 centimetres".
0123456789101112crayonStart at 0. The crayon ends at 7. It is 7 cm long.
The crayon starts at 0 and ends at 7. It is 7 cm long.
Worked example

Example 1: Measure a crayon

Look at the crayon above the ruler. How long is it?

  1. The left end of the crayon lines up with 0.
  2. The right end lines up with 7.

The crayon is 7 cm long.

What if you don't start at 0?

Sometimes the object starts at a different number, or the end of your ruler is broken. Then you can't just read the last number!

Instead, count the spaces (the centimetres) from one end of the object to the other.

0123456789101112eraserFrom 3 to 9: count the spaces. 6 cm.
This eraser starts at 3 and ends at 9.
Worked example

Example 2: The eraser does not start at 0

The eraser starts at 3 and ends at 9. How long is it?

  1. Don't say 9! The eraser does not start at 0.
  2. Count the jumps from 3 to 9: 3 to 4 is 1, 4 to 5 is 2, 5 to 6 is 3, 6 to 7 is 4, 7 to 8 is 5, 8 to 9 is 6.
  3. Or subtract: 9 − 3 = 6.

The eraser is 6 cm long.

eraser0123456789101112123456
Count the jumps (spaces), not the numbers: 6 jumps from 3 to 9.

Count spaces, not lines

A common mistake is to count the number marks instead of the spaces. From 3 to 9 there are 7 number marks (3, 4, 5, 6, 7, 8, 9) but only 6 spaces. Each space is 1 cm, so count the spaces!

4567891011121314keyBroken ruler starts at 4. From 5 to 9 is 4 cm.
This ruler is broken, so it starts at 4. The key goes from 5 to 9: that is 4 cm.
Worked example

Example 3: Draw a line 5 cm long

Draw a straight line that is exactly 5 cm long.

  1. Put your ruler flat on the paper. Hold it still with one hand.
  2. Put your pencil on the 0 mark and make a dot.
  3. Find the 5. Make a dot there.
  4. Slide your pencil along the edge of the ruler from the first dot to the second dot.
  5. Check: measure your line. It should be 5 cm.

A straight line from 0 to 5 is 5 cm long.

Measuring longer things in metres

A ruler is too short for a bed or a room. Use a metre stick or a measuring tape.

To measure with a metre stick: put it down at the start, mark where it ends with your finger, then move it so the start is at your finger. Count how many metre sticks you used. Make sure there are no gaps or overlaps, just like with other units!

Worked example

Example 4: How long is the couch?

Lina measures the couch with a metre stick. She lays it down 2 times, and the couch ends right at the end of the second metre stick. How long is the couch?

  1. Each metre stick is 1 m long.
  2. She used 2 metre sticks: 1 m + 1 m = 2 m.

The couch is 2 m long. That is the same as 200 cm.

Careful and patient

Measuring takes care. If you get a different answer the second time, that's OK! Check: Did you start at 0? Is the ruler straight? Did the ruler slip? Good measurers check their work.

Just for fun

Did you hear about the ruler who became king?

He was a very good... ruler!

Hands-on activity

Ruler challenge

You need: a ruler, paper, a pencil, a few small objects (crayon, spoon, eraser, toy car, key).

  1. Estimate each object's length in centimetres using your fingertip benchmark. Write it down.
  2. Measure each one with the ruler, starting at 0. Write the real length beside your estimate. How close were you?
  3. Now measure the spoon again, starting at 5 on the ruler. Count the spaces. Did you get the same answer?
  4. Draw lines that are 3 cm, 8 cm and 12 cm long. Ask a grown-up to check them.
  5. Bonus: use a measuring tape to find the length of your bed in metres and centimetres.

Math talk: "How did you measure when you didn't start at 0?"

Your turn

1

Where on the ruler do you line up the end of the object?

2

A pencil starts at 0 and ends at 12. How long is it?

3

A toy car starts at 2 and ends at 8. How long is it?

4

A key starts at 4 and ends at 9. Max says it is 9 cm long. Is he right?

5

How would you draw a line 4 cm long?

6

Which tool would you use to measure the length of a room: a ruler or a measuring tape?

More practice: warm-up

1

An eraser starts at 0 and ends at 5. How long is it?

2

A paper clip starts at 0 and ends at 3. How long is it?

3

What unit does a ruler usually show?

4

How long is a metre stick?

5

Should your ruler be straight or tipped when you measure?

More practice: on your own

1

A leaf starts at 1 and ends at 8. How long is the leaf?

2

A broken ruler starts at 3. A crayon lines up from 3 to 12. How long is the crayon?

3

Zoe counted the number marks from 2 to 6 and said the ribbon is 5 cm. What did she do wrong?

4

A table is 1 metre stick long plus 20 cm more. How many centimetres long is it?

5

You draw a line from 0 to 6, then keep going 3 cm more. Where do you stop, and how long is the line?

Challenge

1

A worm starts at 7 and ends at 15 on a ruler. Another worm starts at 0 and ends at 9. Which worm is longer? By how much?

2

A ribbon is 3 metre sticks long. How many centimetres is that?

3

Draw a line 10 cm long, without starting at 0. Tell where you started and where you stopped.

Check your understanding

Quiz

1.

When measuring with a ruler, line up the end of the object with...

2.

A crayon starts at 0 and ends at 8. How long is it?

3.

A shell starts at 2 and ends at 7. How long is it?

4.

A broken ruler starts at 4. A pin goes from 4 to 10. How long is the pin?

5.

To draw a line 6 cm long, you draw from 0 to...

6.

Which tool is best for measuring the length of a hallway?

For parents and teachers

Big idea: A ruler is a row of 1-cm units. Children line up the 0 mark with one end and read the other end. When the object doesn't start at 0, they count the spaces (or subtract). This shows they understand what the numbers on a ruler mean.

Common difficulties:

  • Starting at the edge of the ruler or at 1 instead of 0. Point to the 0 mark on your ruler. Many rulers have a small blank bit before it.
  • Counting the number marks instead of the spaces (getting one too many). Have them hop a finger from mark to mark, counting each hop.
  • Ruler slipping when drawing. Show them how to press down with the non-writing hand spread out.

How to help: Measure toys, cutlery and leaves together. Give your child a "broken ruler" challenge: cover the first few centimetres with a sticky note and measure anyway. Ask "How do you know?"