Circle area calculator

Calculate the area of a circle from its radius using A = πr². Enter a measurement, see the result in square units and check a worked example.

Result

Double the radius, quadruple the area

Area grows with the square of the radius. Increasing the radius from 5 to 10 cm takes the area from about 78.54 to 314.16 cm². Try dragging the blue point.

How do you calculate the area of a circle?

The radius joins the centre to the edge. Area measures the surface inside: multiply π by the radius squared. The diameter passes through the centre and equals two radii; circumference measures the boundary.

Doubling the radius doubles the circumference and multiplies the area by four.

Formula

A = π \times r^{2}

Example and interpretation

A circular coaster has a radius of 5 cm, so its diameter is 10 cm. Squaring the radius gives 25 cm²; multiplying by π gives an area of approximately 78.54 cm².

Practical example

Input: $r = 5 cm$
Result: $≈ 78.54 {cm}^{2}$

Calculation steps

Substitute the example values into the formula.
$A = π \times 5^{2} = 25 π {cm}^{2}$

How to get the area in square metres

Area units are squared. A radius of 5 cm equals 0.05 m and gives the same surface: approximately 0.007854 m². To convert cm² to m², divide by 10,000, not 100. Choose the result unit to perform the conversion.

Precision and limits

Results are normally rounded to two decimal places; very small measurements retain useful digits. Calculations use browser precision; the coefficient in the π form may be rounded. Maximum radius 10¹², input area up to π × 10²⁴. Zero represents a degenerate circle. The drawing fits the measurements and keeps its scale fixed while dragging.

If a change of mode or input unit exceeds numerical limits, it is rejected and the previous measurements are kept. Positive values too small to represent are not treated as zero. Edit a measurement or choose another option to resume calculation.

We count which tools are used most, without including entered values or file contents in the statistics. Privacy

Circle area calculator

Result

Double the radius, quadruple the area

How do you calculate the area of a circle?

Formula

Example and interpretation

Practical example

Calculation steps

How to get the area in square metres

You might also need

Circle circumference

Triangle area

Trapezoid area