Rectangle Area Calculator

The formula

Area = length × width

Both measurements must be in the same unit; the result is in that unit squared. A square is a rectangle whose sides are equal: area = side².

Worked example: flooring a room

A bedroom 4.2 m long and 3.5 m wide has an area of 4.2 × 3.5 = 14.7 m².

When buying flooring or tiles, add a waste allowance for cuts and breakage:

• Straight-laid floating floor or carpet: +5 to 10% → about 16 m².
• Diagonal or herringbone laying, large tiles: +10 to 15%.

Products are sold by the box, so divide by the coverage per box and round up.

Worked example: painting walls

The wall area is the perimeter times the ceiling height, minus openings:

• Perimeter: 2 × (4.2 + 3.5) = 15.4 m
• Walls: 15.4 × 2.5 m = 38.5 m²
• Minus a door (about 1.6 m²) and a window (about 1.5 m²): 35.4 m²

With paint covering about 10 m² per litre and two coats, plan on roughly 7 litres.

L-shaped and irregular rooms

Split the room into rectangles, calculate each one and add them up. An L-shaped living room made of a 6 × 4 m rectangle and a 3 × 2.5 m rectangle measures 24 + 7.5 = 31.5 m².

Units and conversions

• 1 m² = 10,000 cm² (100 × 100), not 100.
• 1 m² ≈ 10.76 ft²: use the area converter for imperial units.
• Hectares and acres are used for land: 1 ha = 10,000 m², the area of a 100 m × 100 m square.

For property, legal floor-area definitions (such as France's "loi Carrez") exclude certain areas, for example where the ceiling is lower than 1.80 m — your own measurement may differ from the official figure.

Formulas and content last reviewed: October 2026 · About