Perimeter
- The perimeter is the distance around the outside of a shape. Add up all the sides.
- A rectangle 8 cm by 5 cm has a perimeter of 8 + 5 + 8 + 5 = 26 cm.
Area
- Rectangle: length × width. A rectangle 8 cm by 5 cm has an area of 40 cm².
- Triangle: ½ × base × perpendicular height. Parallelogram: base × perpendicular height.
- Trapezium: ½ × (a + b) × h, where a and b are the parallel sides.
- Compound shapes: split them into rectangles and triangles, then add the areas.
- Area is measured in square units, such as cm² and m². 1 m² = 10 000 cm².
Circles
- Circumference = π × diameter (or 2 × π × radius). With π = 3.14, a circle with a diameter of 10 cm has a circumference of 31.4 cm.
- Area = π × radius². A circle with a radius of 10 cm has an area of 3.14 × 100 = 314 cm².
- π (pi) is about 3.14. Use the π button on a calculator for more accuracy.
Key terms
- Perimeter
- The distance around the outside of a shape.
- Area
- The amount of space inside a 2D shape.
- Perpendicular height
- The height measured at right angles to the base.
- Circumference
- The distance around a circle.
- Pi (π)
- The ratio of a circle's circumference to its diameter, about 3.14.
- Compound shape
- A shape made from two or more simpler shapes.
- Square centimetre
- A unit of area: a square with sides of 1 cm (cm²).