Measure of a Surface Area

Measure of a Surface Area

Number that expresses an area. This number is related to the unit of measure used.


The area of a circle is a number that expresses the measure of the surface area of the circle.

  • The formula to calculate this measure is: A = π\({r^2}\) = π\(\frac{d^2}{4}\).
  • The letter A represents the area of the circle.
  • The letter r represents the radius of the circle.
  • The letter d represents the diameter of the circle.
  • The value of π is approximately 3.1416.


  • To measure the rectangular surface area below, any of the four unconventional units of measure identified by the letters A to D can be used.
    The area of the blue rectangle is equal to 4 A units, 8 B units, 24 C units or 48 D units.
  • Consider the circle below with a radius of 3 cm.

A = π\({r^2}\)
A ≈ 3.1416 × 3 × 3
A ≈ 28.2744 cm\(^{2}\)

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