# 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.

### Formula

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.

### Examples

• 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$$^{2}$$