Rectangle Calculator: Area, Perimeter and Diagonal
Enter the length and breadth and pick a unit. The area, perimeter and diagonal update as you type.
- Nothing you type is stored
- Free
- No signup
Area
60m²
- Perimeter
- 34 m
- Diagonal
- 13 m
- Diagonal angle with length
- 22.62 °
Show working
- A = l × b = 12 × 5 = 60 m²
- P = 2(l + b) = 2 × (12 + 5) = 34 m
- d = √(l² + b²) = √(144 + 25) = 13 m
How to use
- Enter the length and breadth.
- Choose a length unit.
- Read the area, perimeter and diagonal; open "Show working" for the steps.
Good to know
Area = l × b, perimeter = 2(l + b), and the diagonal follows from Pythagoras: d = √(l² + b²). These are NCERT Class 6–7 mensuration basics.
The diagonal angle is the angle the diagonal makes with the length. It helps when cutting a brace, checking a TV or screen size, or fitting a long item into a box.
Use the same unit for both sides. For floors and plots, enter feet and read the area in ft², or metres for m². Tiles and paint are bought by area, skirting and fencing by perimeter.
Questions
How do I find the diagonal of a rectangle?
d = √(l² + b²). A 12 × 5 rectangle has a diagonal of √169 = 13.
What is the perimeter of a rectangle?
P = 2 × (length + breadth).
How do I check a room is truly rectangular?
Measure both diagonals. If they are equal, the corners are square.
Is a square a rectangle?
Yes, a square is a rectangle with equal sides. Use the square calculator if you know only one value.
Is anything I enter stored?
No. The calculation runs in your browser and nothing is sent to a server.