Desc: Computes area, perimeter, and diagonal of any rectangle from length and width using A = L×W, P = 2(L+W), and d = √(L²+W²). Unit-agnostic with practical applications in room measurement, real estate, flooring, screen sizing, and garden planning.
Calculate area, perimeter, and diagonal of a rectangle from length and width.
The rectangle area calculator computes the area, perimeter, and diagonal of any rectangle from its length and width. The most fundamental geometry calculation — used in construction, real estate, flooring, and everyday measurement.
| L × W | Area | Perimeter | Diagonal |
|---|---|---|---|
| 10 × 12 | 120 | 44 | 15.62 |
| 15 × 20 | 300 | 70 | 25 |
| 8 × 10 | 80 | 36 | 12.81 |
Area = Length × Width. It is that simple. A 12 ft × 15 ft room = 180 square feet.
Diagonal = √(L² + W²) — the Pythagorean theorem. A 10 × 12 rectangle has a diagonal of √(100+144) = √244 = 15.62.
Area measures the space inside (in square units). Perimeter measures the distance around the outside (in linear units). Area = L×W. Perimeter = 2(L+W).
Measure length and width in feet. Multiply them. A 12×15 foot room = 180 square feet. For L-shaped rooms, divide into two rectangles and add the areas.
For L-shapes, T-shapes, or irregular rooms: divide into rectangles, calculate each area, and add them together. For circles, use our Circle Area Calculator.
Yes, completely free. Calculate area, perimeter, and diagonal from length and width.