Perimeter and Area

Prerequisite Knowledge

• choose and use appropriate standard units to estimate and measure length/height in any direction (m/cm); mass (kg/g); temperature (°C); capacity (litres/ml) to the nearest appropriate
• unit, using rulers, scales, thermometers and measuring vessels
• compare and order lengths, mass, volume/capacity and record the results using >, < and =
• measure, compare, add and subtract: lengths (m/cm/mm); mass (kg/g); volume/capacity (l/ml)

Success Criteria

know and apply formulae to calculate:

• rectangles
• rectilinear composite shapes
• area of triangles
• parallelograms
• trapezia

calculate the perimeters of 2D shapes, including composite shapes;

Key Concepts

• Perimeter is a measure of length around the outside of a shape whereas area is the space on a surface.
• Students should be given the opportunity to derive formulae to calculate the area and perimeter of shapes.
• Area is measured in square units.
• Demonstrate a triangle as being half a rectangle so students know to use the perpendicular height in their calculation.
• Demonstrate a parallelogram as having an equal area to a rectangle.
• To calculate the area of composite rectilinear shapes have students break them up in different ways.

Common Misconceptions

• Students often confuse area and perimeter.
• Students can forget to include correct units when stating an area or perimeter.
• When calculating the area of a triangle or parallelogram students tend to use the slanted height rather than the correct perpendicular height.