Rectangle Calculator (A = l×w)
Rectangle area, perimeter and diagonal: A = l×w, P = 2(l+w), d = √(l²+w²).
- Example: 8×4 m → 32 m², 24 m, 8.94 m.
- Free instant results.
Figures are estimates from this calculator’s standard formula — adjust the inputs in the tool below for your exact number.
How the Rectangle Calculator Works
Multiply length by width for area, add then double for perimeter, and apply Pythagoras for the diagonal. Worked example: an 8 × 4 m room has A = 32 m², P = 2(8+4) = 24 m of skirting, and diagonal d = √(64+16) = 8.94 m across the corners.
- 1
Enter length and width
Any unit: m, cm, ft, in.
- 2
Choose the unit scale
Area returns squared, perimeter linear.
- 3
Read the results
Area, perimeter and diagonal computed at once.
Use Cases
Flooring, paint and tile quantity estimates
Fencing and skirting board lengths
Screen and paper aspect-ratio checks
Verifying square corners with the 3-4-5 diagonal rule
Tips
- 1
The diagonal turns any rectangle into two right triangles
- 2
Square meters (m²) for area, meters (m) for perimeter
- 3
8 × 4 ft sheets: keep ft in, get ft² and ft out
Common Mistakes
Adding length and width instead of multiplying for area
Confusing perimeter with area units
Doubling only one side in P = 2(l+w)
Using the diagonal as a side when ordering materials
FAQs
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