CalcRectangle Area Calculator
Last updated: 2026-05-09
The Rectangle Area Calculator is a free online math calculator. Calculate the area, perimeter and diagonal of a rectangle. Get instant results with the detailed formula and step-by-step examples.
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Common Sizes — Click to Fill
| Length (m) | Width (m) | |
|---|---|---|
| Triangulo 3m lado | 2.0 m | 1.2 m |
| Cuadrado 5m lado | 3.5 m | 2.1 m |
| Pentagono 6m lado | 5.0 m | 3.0 m |
| Hexagono 8m lado | 7.5 m | 4.5 m |
| Octogono 10m lado | 12.5 m | 7.5 m |
What is rectangle area?
Rectangle area measures the flat surface a rectangle occupies, expressed in square units (m², cm², ft²…). It's one of the most widely used calculations in architecture, construction, interior design, and school geometry — because most rooms, floors, walls, and plots of land are rectangular.
Rectangle area formula
Area = length × width
For perimeter: Perimeter = 2 × (length + width)
Both dimensions must be in the same unit. If length is in meters and width in centimeters, convert to a common unit first.
Step-by-step example
You want to tile a living room 6.5 m long and 4.2 m wide.
- Area = 6.5 × 4.2 = 27.3 m²
- Add 10% for cuts and waste: 27.3 × 1.10 = 30 m² of tiles to buy
- Perimeter (for baseboard trim): 2 × (6.5 + 4.2) = 21.4 linear meters
Common practical uses
- Flooring and tiling: Calculate how many square meters of hardwood, ceramic, or carpet you need.
- Ceiling and wall paint: One liter of paint covers roughly 8–12 m²; divide the area by that figure to find how many liters to buy.
- Gardens and land: Determine the amount of sod, decorative gravel, or topsoil needed.
- Solar panel installation: Check if available roof area can accommodate the required number of panels.
- Furniture layout: Verify whether a sofa, bed, or table fits in the available floor space.
Common mistakes to avoid
- Mixed units: Mixing meters and centimeters without converting gives results 100 times too large or small.
- Diagonal vs. side: The rectangle's diagonal (√(a²+b²)) is always longer than its sides — don't use it as length or width.
- Forgetting waste allowance: In construction, always add 5–10% to the calculated area for cuts and breakage.
- Rooms with cutouts: Calculate the full rectangle area and subtract the area of any columns or recesses.