Rectangle Area Calculator
Find the area, perimeter and diagonal of a rectangle or square.
What the Rectangle Area Calculator does
Area is width times height, in square units. The diagonal comes from the Pythagorean theorem, which is how you check a frame or room is truly square: equal diagonals mean right angles.
Formula
Area = w × hPerimeter = 2(w + h)Diagonal = √(w² + h²)
Inputs explained
| Input | Unit | Required | Notes |
|---|---|---|---|
| Width | number | Yes | Accepts more than 0. |
| Height | number | Yes | Accepts more than 0. |
How to use it
- Enter Width and Height.
- Select Calculate.
Worked example
A room measuring 4.5 m by 3.2 m.
- Width
- 4.5
- Height
- 3.2
Area 14.4 m², perimeter 15.4 m, diagonal ≈ 5.52 m.
Reading the result
- Equal diagonals prove the corners are right angles, which is the standard site check that a frame or room is truly square.
- Area scales with the product of both sides, so doubling one side doubles the area but doubling both quadruples it.
Common mistakes
- Mixing units between the two sides, such as entering one in metres and the other in centimetres.
- Ordering materials by perimeter when the job is priced by area, or the reverse.
Frequently asked questions
How do I convert square metres to square feet?
Multiply by 10.7639. Note the conversion is squared — 1 m = 3.28 ft, but 1 m² = 10.76 ft².