MEPX
Chapter 3 of 10All chapters
  1. 1Angles
  2. 2Triangles
  3. 3Area and perimeter
  4. 4Circles
  5. 5Similarity and scale
  6. 6Three dimensions
  7. 7Trigonometry
  8. 8Coordinate geometry
  9. 9Transformations
  10. 10Geometry in the world

Chapter 3 of 10

Area and perimeter

Formulas worth memorising.

The short list

Rectangle: length times width. Triangle: half base times height. Parallelogram: base times height. Trapezium: average of the parallel sides times the height.

  • The height is always perpendicular to the base, never the slanted edge.
  • Split awkward shapes into rectangles and triangles rather than hunting a formula.

Units

Perimeter is a length, area is a length squared, volume is a length cubed. Getting the units right catches most arithmetic errors on its own.