Area, perimeter & diagonal — instantly, in any unit
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Use this free rectangle calculator to find the area, perimeter, and diagonal of any rectangle in seconds. Enter the width and height in your preferred unit — meters, centimeters, feet, inches, and more — and the tool instantly applies the standard geometric formulas. Results update live and can be copied with one click, making it ideal for homework, construction, and design projects.
Multiply the width by the height: Area = width × height. For example, a rectangle 8 m wide and 5 m tall has an area of 40 m².
The perimeter equals twice the sum of width and height: Perimeter = 2 × (width + height). A rectangle 8 m × 5 m has a perimeter of 26 m.
Apply the Pythagorean theorem: Diagonal = √(width² + height²). This gives the straight-line distance between opposite corners.
Yes. Select your input unit (e.g. feet) and a different output unit (e.g. meters) — the calculator converts all results automatically so you never have to do manual unit conversions.