Use the formula: A = πr²
A = area
π = pi, about 3.14159
r = radius
Square the radius
Multiply by π
Example: if r = 5, then A = π × 5² = 78.54 square units
Use the formula: A = πr²
A = area
π = pi, about 3.14159
r = radius
Square the radius
Multiply by π
Example: if r = 5, then A = π × 5² = 78.54 square units