CodeKitHubWhat Is This Tool?
An area calculator applies the right geometric formula to a shape's dimensions and returns the surface it covers. A rectangle multiplies width by height; a circle uses π times the radius squared; a triangle is half of base times height; a trapezoid averages the two parallel sides and multiplies by the height. Getting the formula right — and not mixing up radius with diameter — is the part people usually get wrong doing it by hand.
Area shows up constantly outside of math class: how many square meters of flooring to order, how much paint a wall needs, how much fertilizer a lawn requires, or how big a rug should be for a room. This tool covers the four shapes that come up most often in those situations.
Why Use It?
- Four shapes in one tool: rectangle/square, circle, triangle and trapezoid.
- Switch instantly between square meters (m²) and square feet (ft²).
- Results update live as you type — no button to press.
- Handles decimals, so measurements like 3.45 m or 12.5 ft work fine.
- Free and private — the calculation runs entirely in your browser.
How to Use
- Pick the shape tab that matches what you're measuring.
- Enter the required dimensions — for example width and height for a rectangle, or radius for a circle.
- Read the area, shown instantly and updated as you adjust the numbers.
- Switch units between m² and ft² if you need the other measurement system.
Example
Input
Rectangular room, 4.2 m wide and 5 m longOutput
21 m² (about 226 ft²)Area = width × height = 4.2 × 5 = 21 m². Multiply by 10.764 to get the equivalent in square feet.
Area formulas at a glance
| Shape | Formula | Needs |
|---|---|---|
| Rectangle/Square | width × height | width, height |
| Circle | π × radius² | radius |
| Triangle | (base × height) ÷ 2 | base, height |
| Trapezoid | ((a + b) ÷ 2) × height | two parallel sides, height |
Related tools
For converting the resulting area or its dimensions to a different measurement system, or for other everyday calculations, these tools pair well with the area calculator.
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Frequently Asked Questions
How do I calculate the area of a rectangle?
Multiply the width by the height: area = width × height. A room that's 4 meters wide and 5 meters long has an area of 4 × 5 = 20 m². For a square, both sides are equal, so area = side × side (side²).
How do I calculate the area of a circle?
Use area = π × radius². If you only know the diameter, divide it by 2 first to get the radius. A circle with a 3-meter radius has an area of π × 3² ≈ 28.27 m². Be careful not to plug the diameter directly into the formula — that's the most common mistake.
How do I calculate the area of a triangle?
Area = (base × height) ÷ 2, where the height is measured perpendicular to the base, not along one of the slanted sides. A triangle with a 6-meter base and a 4-meter height has an area of (6 × 4) ÷ 2 = 12 m².
How do I calculate the area of a trapezoid?
Add the two parallel sides, divide by 2, and multiply by the height: area = ((a + b) ÷ 2) × h. For a trapezoid with parallel sides of 6 m and 4 m and a height of 3 m, that's ((6 + 4) ÷ 2) × 3 = 15 m².
How can this help with a home renovation project?
Most renovation materials — flooring, tiles, paint, wallpaper, turf — are sold by area. Measure the room or wall with the matching shape (usually a rectangle, or several rectangles added together for an irregular room), calculate the area, and add roughly 10% extra for cuts and waste before ordering.
Is my data stored anywhere?
No. The calculation runs entirely in your browser with JavaScript; nothing you enter is sent to a server, stored or logged.