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Geometry

Circle Area Calculator

Find the area of a circle from its radius.

Let’s calculate.

Popularity
Circle area
—square units
Rounded to up to 2 decimal places.

Measurement units

Changing the input unit also selects its matching result unit. Choose another result unit to convert the answer. Input numbers stay unchanged.

SI prefixes and selected international / customary units. Coverage: SI and selected current customary units. Historical units are excluded.

See what you’re calculating

rArea
Area = π × r²

The shaded region is the area. Radius r runs from the centre to the edge.

Illustration not to scale.

No account needed. Your inputs stay in this browser.

THE IDEA, SIMPLY

How it works

The radius is the distance from the centre to the edge. Square it and multiply by pi to find the area.

FORMULA

Area = π × r²

A worked example

A radius of 5 gives an area of 25π ≈ 78.5398163397 square units.

Formula & detailed explanation

The radius r must be nonnegative. Area is expressed in square units: a radius in metres produces an area in square metres. Pi is evaluated to 40 significant digits internally; displayed results are rounded.

Calculations use decimal arithmetic with 40 significant digits internally. Choose 0–8 decimal places for the displayed result. Trailing zeros are omitted. Rounding affects only the displayed and copied result; very small values may round to zero. Accepted inputs have up to 100 characters and magnitudes from 10⁻¹⁰⁰ to 10¹⁰⁰, plus zero.

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