How to use the Rectangle Area Calculator
Enter the width and the height in the same unit.
The rectangle area formula
Area = width × height. A room 4 m wide and 5 m long has an area of 20 m². A square is a rectangle with equal sides, so a 3 m square is 9 m².
Mixed units and L-shaped rooms
Convert both sides to the same unit before multiplying: 12 ft by 30 in is 12 ft by 2.5 ft, or 30 ft². For an L-shaped room, split it into two rectangles, find each area and add them.
The formula
A = width × height
Examples
- 8 by 10
Area: 80
- 15 by 12 (a room in feet)
Area: 180
- 3.5 by 2.4
Area: 8.4
Rectangle area examples
| Width × height | Area |
|---|---|
| 2 × 3 | 6 |
| 4 × 5 | 20 |
| 3.5 × 4.2 | 14.7 |
| 8 × 2.5 | 20 |
| 10 × 10 | 100 |
| 12 × 15 | 180 |
| 20 × 30 | 600 |
| 50 × 100 | 5,000 |
Limitations and assumptions
Both sides must use the same unit. The area comes back in that unit squared.
Frequently asked questions
How do I find the area of a room?
Measure the length and width of the floor in the same unit and multiply them. Many people add about 10% when buying flooring to allow for cutting and waste.
What unit is the area in?
The square of the unit you used: metres give m², feet give ft².
How do I find a missing side?
Divide the area by the known side. A 24 m² rectangle that is 4 m wide is 6 m long.