Circle

Diameter = 2r. Circumference = 2πr. Area = πr². π is JavaScript’s Math.PI. A diameter you type as a radius will be twice too big.

Radius

Area

28.2743

Circumference

18.8496

Diameter

A radius of 1 gives area π. The triangle page is three sides, not a radius.

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An educational estimate. Not medical, tax or credit advice.

Area of any triangle from three sides, if they close.

Sine, cosine and tangent of an angle in degrees, plus the radian.

Fill two sides of a right triangle; the third and the area come out.

What is x percent of y, what percent is a of b, and the percentage change from A to B.

How much a figure moved, as a percent of the starting value.

Real roots of a quadratic, or a linear fallback if a is zero.