Perimeter
- Perimeter is the total distance around the outside of a shape. Add up all the side lengths.
- In a compound shape, work out any missing side lengths first.
Area formulae
- Rectangle: length × width. Triangle: ½ × base × perpendicular height.
- Parallelogram: base × perpendicular height. Trapezium: ½(a + b)h, where a and b are the parallel sides.
- Always use the perpendicular height (at right angles to the base), not a slanted side.
Compound shapes
- Split the shape into rectangles and triangles, find each area, then add them. Subtract any parts that are cut out.
- An L-shape made from a 10 cm by 8 cm rectangle with a 4 cm by 3 cm corner cut out has an area of 80 − 12 = 68 cm².
Units
- Area is measured in square units, such as mm², cm² and m². Perimeter is a length, measured in mm, cm or m.
- 1 cm² = 100 mm², and 1 m² = 10 000 cm².
Key terms
- Perimeter
- The total distance around the outside of a shape.
- Area
- The amount of space inside a flat shape.
- Perpendicular height
- The height measured at right angles to the base.
- Parallelogram
- A quadrilateral with two pairs of parallel sides.
- Compound shape
- A shape made from two or more simple shapes.
- Square units
- Units for area, such as cm² and m².