How do I calculate the area of a circle?

A = πr² and the circumference is C = 2πr. Enter the radius under “Circle” and the diameter is given too.

Can I get a triangle’s area from three sides?

Yes — choose “Triangle (three sides)” to use Heron’s formula A = √[s(s-a)(s-b)(s-c)] with s the semi-perimeter. The circumradius and inradius are included.

What are the surface area formulas for a cylinder and a cone?

Cylinder: S = 2πr(r+h). Cone: S = πr(r+l) where the slant height l = √(r²+h²), which the tool computes for you.

What units are the results in?

Values are unit-free: whatever unit you use for lengths, areas come out squared and volumes cubed — centimetres give cm² and cm³.

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📐Geometry Calculator - Area, Perimeter, Volume and Surface Area

Pick a shape, type the dimensions and get the area, perimeter, volume and surface area at once, along with extras such as diagonals, circumradius and slant height — and the formula used, ready to copy into your homework.

Free · No sign-up · Runs in your browserLast updated: 2026-10-26

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How to use Geometry Calculator

1Choose 2D shapes or 3D shapes
2Pick the shape — circle, trapezoid, cone and so on
3Enter the dimensions; results update as you type

FAQ

How do I calculate the area of a circle?: A = πr² and the circumference is C = 2πr. Enter the radius under “Circle” and the diameter is given too.
Can I get a triangle’s area from three sides?: Yes — choose “Triangle (three sides)” to use Heron’s formula A = √[s(s-a)(s-b)(s-c)] with s the semi-perimeter. The circumradius and inradius are included.
What are the surface area formulas for a cylinder and a cone?: Cylinder: S = 2πr(r+h). Cone: S = πr(r+l) where the slant height l = √(r²+h²), which the tool computes for you.
What units are the results in?: Values are unit-free: whatever unit you use for lengths, areas come out squared and volumes cubed — centimetres give cm² and cm³.