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 works right here on your device — nothing gets sent out.
Enter every dimension in the selected dimension unit. The result converts to your chosen square unit.
How it works
- Choose a shape from the dropdown.
- Choose the unit your measurements use and the square unit you want for the answer.
- Enter the dimensions — the fields change to match the selected shape.
- The formula and converted area update instantly as you type or change units.
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 m long and 5 m wide has an area of 8 × 5 = 40 m². You can show that same area as about 430.56 ft².
FAQ
Does anything I type get sent anywhere?
No. Every calculation happens locally in your browser — nothing is uploaded or logged.
Can I convert the area to different units?
Yes. Choose the unit used for every dimension, then choose the square unit for the result. The calculator converts the area without changing your entered dimensions.
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 | CodeKitHub | ArrayKit | CalcDuck |
|---|---|---|---|---|
| Shows the formula with your entered dimensions | ✓ | Formula reference only | Formula reference only | Formula reference only |
| Convert area between seven squared units | ✓ | m² and ft² | No conversion | No conversion |
All dimensions must use the selected input unit. Only the calculated area is converted; your measurements are not changed. Calculations run locally in your browser.