Rectangle Calculator
Calculate the area, perimeter, and diagonal length of a rectangle from its length and width.
- Free to use
- Accurate results
- No registration required
- Works on all devices
Enter a rectangle's length and width to calculate its area, perimeter, and diagonal.
Your result
40
Area
Perimeter26
Diagonal9.434
AI explanation
Formula
Area = length × width; Perimeter = 2(length + width); Diagonal = √(length² + width²)Worked example
8 x 5 rectangle
| Field | Value |
|---|---|
| Length | 8 |
| Width | 5 |
| Area | 40 |
| Perimeter | 26 |
| Diagonal | 9.434 |
Assumptions
- A square is a special case of a rectangle with equal length and width — see the Square Area Calculator for a single-field version.
Frequently asked questions
How is the diagonal of a rectangle calculated?
By the Pythagorean theorem — the diagonal splits the rectangle into two right triangles, so diagonal = √(length² + width²).
What's the difference between area and perimeter?
Area measures the space enclosed inside the rectangle (in square units). Perimeter measures the total distance around its edges (in linear units).
How do I calculate a square's area with just one measurement?
Use the Square Area Calculator, which only asks for the side length since all four sides of a square are equal.