Grade 3 · Math · Unit 10 of 13
Length & Perimeter
Metres, centimetres and the distance around a shape.
What your child practises
Measuring length in millimetres, centimetres, decimetres and metres, the imperial units inch, foot and yard, estimating with benchmarks, and finding the perimeter of polygons.
Prince Edward Island Curriculum curriculum outcome: SS5 · measuring the distance around a shape to find its perimeter
How we explain it
Children can open this short lesson before they practise.
- 10 mm make 1 cm. 10 cm make 1 dm. 100 cm make 1 m.
- Line up the 0 of the ruler with one end.
- Perimeter is all the sides added together.
Example: 6 dm is how many cm? 1 dm is 10 cm. 6 × 10 = 60. Answer: 60 cm
Sample questions
A taste of this unit. In the app, questions change every time and get easier or harder to match your child.
Question 1
A rectangle is 15 cm long and 11 cm wide. What is its perimeter in cm?
answer boxcm
52 cm
Hint: Add all four sides: length + width + length + width.
Question 2
Which unit is best for measuring the length of your foot?
- millimetres
- metres
- centimetres
centimetres
Hint: Pick a unit that gives a number that is not too big and not too small.
Question 3
7 dm is how many cm?
answer boxcm
70 cm
Hint: 1 decimetre (dm) is 10 cm.
Question 4
About how long is the width of your hand?
- about 8 cm
- about 80 cm
- about 8 m
about 8 cm
Hint: Use something you know as a measuring stick. A doorway is about 2 m tall.
Question 5
A square garden has a perimeter of 44 m. How long is one side in m?
answer boxm
11 m
Hint: A square has 4 equal sides. Share the perimeter into 4 equal parts.
Question 6
A triangle has sides of 10 cm, 10 cm and 8 cm. What is its perimeter in cm?
answer boxcm
28 cm
Hint: The perimeter is the distance around. Add all the sides.