Measure and compare length in metres

What you will learn

• Measure and compare length in metres

Models used: number sentences, stories, bar models.

Compare lengths in metres

Two ribbons are 2 metres and 3 metres long. Which is longer?

1. Both bars use the same scale. Compare their lengths and read the names beside them.

   Read the unit with each number. Both measurements use the same unit, so their numbers can be compared.

   2 m2

   3 m3

   Difference: 1

2. Both bars use the same scale. Compare their lengths and read the names beside them.

   3 m is the greater measurement. The longer bar represents the larger amount, not a drawing of the object’s shape.

   3 > 2

   2 m2

   3 m3

   Difference: 1

3. Both bars use the same scale. Compare their lengths and read the names beside them.

   A metre is a length unit. Use a metre rule or tape; measure from zero to the other end.

   3 − 2 = 1 m

   2 m2

   3 m3

   Difference: 1

Worked example: A new example, together

One rope measures 5 m and another 12 m. What is the difference?

1. Both bars use the same scale. Compare their lengths and read the names beside them.

   Check the unit before comparing two lengths.

   Comparing measurements requires matching the amount and unit.

   First rope (m)5

   Second rope (m)12

2. Both bars use the same scale. Compare their lengths and read the names beside them.

   Both measurements use the same unit.

   First rope (m)5

   Second rope (m)12
   One rope measures 5 m and another 12 m. What is the difference?

   7 m

3. Both bars use the same scale. Compare their lengths and read the names beside them.

   12 − 5 = 7.

   First rope (m)5

   Second rope (m)12

4. Both bars use the same scale. Compare their lengths and read the names beside them.

   The difference is 7 m.

   First rope (m)5

   Second rope (m)12

5. Both bars use the same scale. Compare their lengths and read the names beside them.

   Check the result against the question we started with.

   Re-read the labels and unit before comparing the numbers.

   We found 7 m. Comparing measurements requires matching the amount and unit.

   First rope (m)5

   Second rope (m)12

Common mistakes to discuss

• Comparing numbers across different units. Change both amounts to the same unit before comparing. 700 g is less than 1 kg, although 700 is the larger number.

Check your understanding

• Measure and compare length in metres
• connect metres and centimetres
• check the answer against the original quantities and units

Explain your reasoning to an adult, then try a fresh question in the interactive lesson. A result from one attempt is not proof of lasting mastery.