How to use the rectangle calculator
Compute area, perimeter and diagonal of a rectangle. Enter length, width in the fields above; the area, perimeter, diagonal are computed instantly and plotted on the chart so you can see how the answer changes.
Common searches this calculator answers include “area of rectangle”, “room size”, “diagonal length”, “calculate rectangle”, “find area”.
Formula
Variables
- l — Length
- w — Width
Worked example
With length = 12, width = 5, the calculator gives area ≈ 60; perimeter ≈ 34; diagonal ≈ 13.
Frequently asked questions
What is the rectangle calculator used for?
Compute area, perimeter and diagonal of a rectangle. It helps with questions such as “area of rectangle”, “room size”, “diagonal length”.
What is the formula for the rectangle calculation?
Area = l × w. Perimeter = 2 × (l+w). Diagonal = hypot(l,w). Here l is length, w is width.
What inputs do I need for the rectangle calculator?
You need length, width. Each field is pre-filled with a typical example so you can see how the result responds as you edit the numbers.
How do I use the rectangle calculator?
Type values into the input fields. Results and the chart update instantly. Use Reset to restore the example values, Copy results to paste them elsewhere, or Share to copy a link that preserves your inputs.
Is the rectangle result exact?
Calculations use standard formulas and double-precision arithmetic, then display about seven significant figures. Real-world measurements carry uncertainty, so treat results as estimates unless your inputs are exact.