A rectangle is the most common shape in floor plans, screens, and land plots.
About this calculator
A rectangle is the most common shape in floor plans, screens, and land plots. Multiply length by width for area, add all four sides (or use 2(L + W)) for perimeter, and apply the Pythagorean theorem for the corner-to-corner diagonal.
Enter consistent units — metres for a room, feet for a US floor plan, or abstract units for homework. Aspect ratio L:W tells you how elongated the shape is; a 16:9 screen has ratio about 1.78.
Every rectangle is a parallelogram with right angles. For flooring quotes add 10–15% waste on top of the raw area. Link to [[area]] for mixed shapes, [[square-footage]] for room totals, [[parallelogram]] when corners are not 90°, and [[distance]] when corners sit on a coordinate grid.
Common uses
- Room floor area from length and width measurements
- Diagonal brace length across a rectangular frame
- Screen or poster aspect ratio checks
- Garden bed perimeter for fencing material
- Coordinate geometry — verify area of an axis-aligned box
Frequently asked questions
What is the area of a 10 × 5 rectangle?
Area = 10 × 5 = 50 square units. Perimeter = 2(10 + 5) = 30 units. Diagonal = √(100 + 25) ≈ 11.18 units.
How do I find the diagonal?
Treat length and width as legs of a right triangle. Diagonal = √(L² + W²). This matches the [[right-triangle]] calculator with legs L and W.
Does length have to be longer than width?
No. Either side can be labeled length or width. Area and perimeter stay the same if you swap the labels.
What is aspect ratio?
It is L divided by W. A square has aspect ratio 1. A 1920×1080 display has ratio 1.78 because 1920/1080 ≈ 1.78.