Area of a Rectangle Calculator
The area of a rectangle is length × width: an 8 m × 5 m room is 40 m², about 430.6 ft².
40 m²
- Area
- 40 m²
- Perimeter
- 26 m
- Diagonal
- 9.43398 m
In other units: 400000 cm² · 40000000 mm² · 0.00004 km² · 0.004 ha · 430.556 ft² · 62000.1 in² · 47.8396 yd² · 0.00988422 ac · 0.0000154441 mi²
Step-by-step solution
- A = l × w
- A = 8 × 5 = 40 m²
Area of a Rectangle Formula
A = l × w
l length, w width
Worked Example
An 8 m × 5 m room:
- A = l × w
- A = 8 × 5 = 40 m²
Perimeter: 26 m · Diagonal: 9.43398 m
Same area in other units: 400000 cm² · 40000000 mm² · 0.00004 km² · 0.004 ha · 430.556 ft²
Measuring and converting rectangular areas
Measure length and width in the same unit; the calculator converts the result to any area unit exactly. For rooms that are not quite square, measure each wall and average the opposite sides, or split an L-shaped room into two rectangles and add them. When buying flooring or tiles, add 5–10 % for cutting waste. Remember that area units scale with the square of length units: 1 m² is 10.764 ft², not 3.281.
Frequently asked questions
How do I calculate the area of a room in square feet?
Measure length and width in feet and multiply: 12 ft × 15 ft = 180 ft². For an L-shaped room, split it into two rectangles and add the areas.
How do I find the width if I know the area and length?
Divide the area by the length: w = A ÷ l. A 60 m² rectangle that is 12 m long is 5 m wide.
What is the formula for the perimeter of a rectangle?
P = 2(l + w). An 8 m × 5 m rectangle has a perimeter of 26 m.
Sources
- The International System of Units (SI), 9th edition (SI Brochure), Bureau International des Poids et Mesures .
- Guide for the Use of the International System of Units (SI), NIST Special Publication 811, 2008 Edition, National Institute of Standards and Technology .
Last reviewed: . Factors are stored exactly and computed with 50-digit decimal arithmetic. See how we verify conversion factors.
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APA
Scientific Converters. (2026, October 15). Area of a Rectangle Calculator. Retrieved October 25, 2026, from https://scientificconverters.com/calculators/area-of-a-rectangle/
IEEE
Scientific Converters, "Area of a Rectangle Calculator," scientificconverters.com. Accessed: Oct. 25, 2026. [Online]. Available: https://scientificconverters.com/calculators/area-of-a-rectangle/