Grade 3 · Unit 5: Using units of measurement

Length, perimeter and area

Around the edge or covering the inside?

Fencing a field

A farmer walks around the edge of a field. The distance around is the perimeter. The ground inside is the area.

Units of length

Choose the unit that fits the size. A millimetre is tiny; a kilometre is long. The Padma Bridge is about 6 km long.

Perimeter

Add all the sides. 5 + 3 + 5 + 3 = 16 units. Or: 2 × (5 + 3) = 16.

Area

Count squares, or multiply rows by columns. 3 × 5 = 15 square units. Perimeter is a length; area is a number of squares.

Millimetres and decimals

Each centimetre has 10 small marks: millimetres. 7 cm and 5 mm is 7.5 cm, or 75 mm. Lengths can be written with decimals: 1.5 m = 1 m 50 cm = 150 cm.

What I learnt

• I can choose mm, cm, m or km.
• I can find perimeter.
• I can find area by counting or multiplying.