# Rectangle Calculator

URL: https://speedycalculator.com/calculators/math/rectangle/
Last updated: 2026-10-25

> The rectangle calculator finds the area, perimeter and diagonal of a rectangle from its length and width, in any units. Type an area to solve for the length.

## Inputs

- Length (m, cm, mm, km, in, ft, yd, mi)
- Width (m, cm, mm, km, in, ft, yd, mi)

## Results

- Area
- Perimeter
- Diagonal

## Formula

```
Area = l × w
Perimeter = 2(l + w)
Diagonal = √(l² + w²)
```

## Explanation

Rectangles are the most common shape in rooms, screens, plots and paper.

### How to use the Rectangle Calculator

- **Length**
- **Width**
- Want to work backwards? Type a value into **Area** and **Length** is calculated for you.

Results update as you type, and every field accepts the units shown in its menu.

### How it works

Multiply length by width for area, add the sides for perimeter and use Pythagoras for the diagonal.

### Inputs explained

FieldWhat to enterLengthUnits: m, cm, mm, km, in, ft …WidthUnits: m, cm, mm, km, in, ft …

### What each result means

- **Area** = [Length] × [Width]
- **Perimeter** = 2×([Length] + [Width])
- **Diagonal** = sqrt([Length]^2 + [Width]^2)

### Example values

How the main result changes when **Length** changes and everything else stays at the example values above:

Length (m)Area (m²)420630840105012601680

## Worked example

Inputs — Length: 8 m; Width: 5 m.

Results — **Area = 40 m²**; Perimeter = 26 m; Diagonal = 9.43 m.

## FAQ

**Is a square a rectangle?**
Yes, a square is a rectangle with equal sides.

**How do I find the area of an L-shaped room?**
Split it into rectangles and add their areas.

**What formula does the Rectangle Calculator use?**
Area = l × w.

**Can I work backwards from the result?**
Yes. Type the result you want into Area and the calculator finds the matching length.