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
| Field | What to enter |
|---|---|
| Length | Units: m, cm, mm, km, in, ft … |
| Width | Units: 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) |
|---|---|
| 4 | 20 |
| 6 | 30 |
| 8 | 40 |
| 10 | 50 |
| 12 | 60 |
| 16 | 80 |
Formula
Area = l × wPerimeter = 2(l + w)Diagonal = √(l² + w²)Worked example
Inputs — Length: 8 m; Width: 5 m.
Results — Area = 40 m²; Perimeter = 26 m; Diagonal = 9.43 m.
Frequently asked questions
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.