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The area of a circle is πr², where r is the radius. Learn the formula, what each part means, and how to find the area from the radius or diameter.
A circle's area grows with the square of its radius. The formula A = πr² says: square the distance from the center to the edge, then multiply by π.
The radius runs from the center to the edge; the diameter crosses the whole circle through the center and is twice the radius. Knowing either one is enough to find the area.
The area of a circle is A = πr², where r is the radius. Square the radius and multiply by π (about 3.14159).
If you know the diameter instead, halve it to get the radius (r = d/2), then apply A = πr². You can also write it as A = π(d/2)².