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

> Free online geometry calculator: area and perimeter of circles, triangles, polygons and more, plus volume and surface area of solids, with the formulas shown.

- URL: https://qilingtools.com/en/math/geometry
- Category: Math Tools (https://qilingtools.com/en/math)
- Tags: [Math](https://qilingtools.com/en/tags/math), [Education](https://qilingtools.com/en/tags/education)
- Last updated: 2026-10-26
- Price: Free, no sign-up
- Privacy: Runs locally in the browser; files are never uploaded

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.

## How to use

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

## Features

- 10 plane shapes and 6 solids
- Triangles by base × height or by three sides (Heron)
- Extras such as diagonals, circumradius, inradius, slant height
- The formula for every shape
- One-click copy for every value

## 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.

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