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Tips for perimeter, area and volume

  • Before you start to work out a perimeter, area or volume, check what units you need the answer in, and make sure that all dimensions are in the same units.
  • Perimeter is the distance around the edge of a shape. Perimeter is a length, measured in mm, cm or m.
  • Area is measured in square units, for example, mm², cm², m².
  • Volume is measured in cubic units, for example, mm³, cm³, m³.
  • The perimeter of a circle is called the circumference. C = πD, where D is the diameter.
  • The area of a circle is given by the formula A = πr² where r is the radius (half the diameter).
  • The volume of a cylinder is given by the formula V = πr²h, where r is the radius of the circular end, and h is the height (or length).
  • The value of π is approximately 3.142, or 3.14. If there are questions in the National Test on circles or cylinders, they may ask you to use π = 3 because you are not allowed to use a calculator. However, this is not a good approximation if you have to do practical calculations because of the margin of error from rounding down.