Online Tool Store
Area Calculator
Calculate rectangle, square, circle, triangle, or trapezoid area with live results and the formula shown beside the answer in your chosen units.
🔒 This tool runs entirely in your browser. Your files are never uploaded to a server.
Use any unit you like — the result is in that same unit, squared.
How it works
- Choose a shape from the dropdown.
- Enter its dimensions — the fields change to match the shape you picked.
- The area, and the formula used to get it, update instantly as you type.
The formulas
Each shape uses a standard geometry formula:
Rectangle = length × width
Square = side²
Circle = π × radius²
Triangle = ½ × base × height
Trapezoid = ½ × (side a + side b) × height
Example: a rectangle 8 units long and 5 units wide has an area of 8 × 5 = 40 square units.
FAQ
Does anything I type get sent anywhere?
No. Every calculation happens locally in your browser — nothing is uploaded or logged.
What units does it use?
Whatever unit you enter — the result is in that same unit, squared. Enter dimensions in metres and the area is in square metres; use inches and it's in square inches.
Which shapes are supported?
Rectangle, square, circle, triangle, and trapezoid — the shapes people most often need an area for.
Why does it reject a 0 or negative value?
A shape's side, radius, base, or height has to be a positive number — 0 or a negative value doesn't describe a real shape, so it's rejected with an error instead of returning a meaningless result.
How accurate is the circle area?
It uses JavaScript's built-in Math.PI, which is accurate to about 15 significant digits — far more precise than the 3.14 or 3.14159 typically used by hand.
How we compare
| Feature | Online Tool Store | Calculator app | CalculatorSoup |
|---|---|---|---|
| No file upload — runs in your browser | ✓ | ✓ | ✓ |
| Shows the formula alongside the result | ✓ | ✗ | ✓ |
| No manual formula entry needed | ✓ | You type the formula yourself | ✓ |
A plain calculator app can get you there, but you have to remember and type the formula yourself. Area Calculator picks the right formula for the shape you choose and shows it alongside the answer, so you can double-check the working, not just trust a number.