Measuring Length, Mass, Capacity and Area
What this lesson covers
- People have measured in many ways. In te ao Māori, lengths were measured with the body.
- Length is measured in cm and m, mass in g and kg, and capacity in mL and L.
- Perimeter is the distance around a shape: add up all the sides.
- Area is how much surface a shape covers. Count the squares.
Measuring long ago
- Long ago, people measured with their bodies: hand spans, steps and arm spans.
- Different cultures measured in different ways. In te ao Māori, lengths were measured with the body, such as the span of outstretched arms.
- Bodies are different sizes. Today we also use units that are the same everywhere: metres, grams and litres.
Units and tools
- Estimate first, then measure and check.
- Start measuring from the 0 mark on the tool.
| Measuring | Units | Tool | Example |
|---|---|---|---|
| length | cm and m | ruler, tape measure | a pencil is about 15 cm |
| mass | g and kg | scales | a bag of sugar is about 1 kg |
| capacity | mL and L | measuring jug | a big milk bottle holds 2 L |
Try it: length, mass or capacity?
Comparing and ordering
- Three pāua shells are 9 cm, 14 cm and 11 cm long.
- Shortest to longest: 9 cm, 11 cm, 14 cm.
- Compare amounts in the same unit. 1 L is 1,000 mL, so 1 L is more than 600 mL.
| Bottle | Holds |
|---|---|
| Juice box | 250 mL |
| Water bottle | 600 mL |
| Milk bottle | 1 L |
Perimeter: the distance around
- Walk around the edge of a shape. That distance is its perimeter.
- Add the lengths of all the sides.
| Shape | Sides | Perimeter |
|---|---|---|
| triangle | 5 cm, 5 cm, 5 cm | 15 cm |
| rectangle | 6 cm, 4 cm, 6 cm, 4 cm | 20 cm |
| square | 3 m, 3 m, 3 m, 3 m | 12 m |
Area: the space inside
- Area is how much surface a shape covers.
- Cover a rectangle with squares of the same size, then count them.
- A rectangle 4 squares long and 3 squares wide has 3 rows of 4: 12 squares.
Try it: count the squares
Common mistakes
- The perimeter of a 6 cm by 4 cm rectangle is 6 + 4 = 10 cm.A rectangle has four sides: 6 + 4 + 6 + 4 = 20 cm.
- Start measuring from the very end of the ruler.Start at the 0 mark, which is not always the very end.
- 900 g is heavier than 2 kg because 900 is bigger.2 kg is 2,000 g, so 2 kg is heavier.
- Count only the squares around the edge to find the area.Area counts every square inside the shape.
Your turn
1
Which unit would you use for the water in a bucket: cm, kg, L or g?
2
Put 3 kg, 500 g and 1 kg in order from lightest to heaviest.
3
What is the perimeter of a rectangle 5 m long and 2 m wide?
4
A rectangle is 5 squares long and 2 squares wide. What is its area?
5
What is the perimeter of a square with sides of 7 cm?
Show answer
1. L 2. 500 g, 1 kg, 3 kg 3. 14 m (5 + 2 + 5 + 2) 4. 10 squares (2 rows of 5) 5. 28 cm (7 + 7 + 7 + 7)
What to take away
- Pick the right unit and tool, and start at 0.
- Perimeter: add all the sides.
- Area: count the squares inside.
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