Primary 1 maths · Measurement & time · About 8 minutes
Measure and compare lengths in centimetres
Locate both endpoints and check the size of one interval.
Start the interactive lesson →Open practice activity
What you will learn
- Measure and compare lengths in centimetres
Models used: number sentences, stories, diagrams.
Begin at zero
Line up one end of the ribbon with zero. Each space on the ruler represents 1 centimetre.
Line up one end of the ribbon with zero. Each space on the ruler represents 1 centimetre.
A length is a distance, not a count of boundary marks. Starting at zero makes the far reading the length.
The ribbon starts at zero and ends at five. Count the spaces between marks: one, two, three, four, five.
Five centimetre intervals span the ribbon. The ribbon is 5 cm long. The zero mark is a starting point, not an extra centimetre.
5 − 0 = 5 cm
The ribbon measures five centimetres.
What did the picture help us see?
The ribbon is 5 cm long. The zero mark is a starting point, not an extra centimetre.
Worked example: A new example, together
Read the length of the ribbon.
Locate both endpoints and check the size of one interval.
Length is the difference between the endpoints on a measurement scale.
The first end is aligned with zero. Locate zero at the first end.
The first end is aligned with zero. Read the length of the ribbon.
7 cm
Locate zero at the first end.
The first end is aligned with zero. Count 7 one-centimetre intervals.
The first end is aligned with zero. The far end is at 7 cm.
The first end is aligned with zero. Check the result against the question we started with.
7 − 0 = 7 cm.
We found 7 cm. Length is the difference between the endpoints on a measurement scale.
The first end is aligned with zero.
Common mistakes to discuss
- Starting at the end of the ruler. Measurement starts at zero. Reading from the edge of the ruler makes every length too long.
Check your understanding
- Measure and compare lengths in centimetres
- measure or draw a length by its endpoints and intervals
- 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.
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