Rectangle area and perimeter calculator
Enter the length and width of a rectangle to get its area, perimeter and diagonal in one step.
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Processing and privacy: The result is calculated inside your browser and your data is not sent to any server.
How to use it
- Enter length, width and length unit.
- The result appears straight away and updates as you edit.
- Copy the result, or copy a link that keeps the same values to share it.
How it is calculated
Area = length × width, perimeter = 2 × (length + width) and diagonal = √(length² + width²).
Example
Inputs: Length = 5, Width = 3, Length unit = Centimeters (cm). Result: Area: 15 cm²; Perimeter: 16 cm; Diagonal: 5.831 cm.
Limits and caveats
- It assumes perfect right angles; irregular rooms should be split into rectangles.
- The unit choice only labels the results.
Questions about this tool
What is the formula for the area of a rectangle?
Area equals length times width. A 5 × 3 m room has an area of 15 m².
What is the difference between area and perimeter?
Area is the surface inside the shape, in square units. Perimeter is the length of the boundary, in length units.
How do I measure an L-shaped room?
Split it into two rectangles, find each area and add them.