Area Calculator Calculators
Area and perimeter for rectangles, circles, triangles and more.
Area Calculator is a free online tool that area and perimeter for rectangles, circles, triangles and more. It runs entirely in your web browser using plain JavaScript, so files are processed on your own device and never uploaded to a server. There is no sign-up, no file size limit imposed by the site, no watermark and no paid tier.
- Price
- Free — no account, no quota, no watermark
- Category
- Calculators
- Where it runs
- In your browser, on your device
- Files uploaded
- None
- Technology
- plain JavaScript
- Settings
- 4
- Works offline
- Yes, after the first visit
About Area Calculator
Circle and ellipse areas use π exactly as the browser stores it, and the ellipse perimeter uses Ramanujan's approximation — there is no closed-form exact expression for it, which surprises people. The triangle option takes base and height rather than three sides, so use the Right Triangle Calculator if that is what you have.
How to use it
- Enter shape, width / radius / base and height / second side.
- Adjust the remaining 1 setting if the defaults do not fit your case.
The 4 settings
| Setting | What it does | Default |
|---|---|---|
| Shape | Choose from 5: Rectangle, Circle, Triangle, Trapezoid, Ellipse. | Rectangle |
| Width / radius / base | A numeric value. | 10 |
| Height / second side | A numeric value. | 6 |
| Third value (if needed) | A numeric value. | 4 |
Under the hood
| Runs on | plain JavaScript — runs the whole thing |
| Controls | Shape, Width / radius / base, Height / second side, Third value (if needed) |
Questions
What units does this use?
Whatever you put in. Feed it centimeters and you get square centimeters. The conversion rows underneath assume centimeters and inches respectively, as the two most common cases.
What does the shape option change?
It offers 5 choices — Rectangle, Circle, Triangle and Trapezoid and more. The default is Rectangle, which suits most cases; change it when your input or your destination calls for something specific.
Is the arithmetic exact?
It uses double-precision floating point — about 15 significant figures, far more than the inputs justify. Displayed rounding is cosmetic; the underlying numbers are not rounded between steps, so chained results do not drift.