Rectangle Area Calculator
Select shape
Rectangle area formula explained
The area of a rectangle is A = width × height. Width and height must use the same unit. If the width is in feet and the height is in feet, the answer is in square feet.
This calculation is common in home improvement, construction estimating, gardening, printing, shipping layouts, wall painting, flooring, and screen measurement. The key is to measure the two perpendicular sides, not the diagonal.
Worked example: room 12 ft by 8 ft
A = w × h
A = 12 × 8
Result: 96 ft²
Practical example: flooring
If a rectangular room is 14 ft long and 10 ft wide, the base area is 140 ft². For flooring, many people add a waste allowance separately because cutting and layout patterns can require extra material.
Common mistakes
- Measuring length and width in different units without converting first.
- Using the diagonal as one side of the rectangle.
- Confusing area with perimeter. Perimeter is 2 × (w + h); area is w × h.
Related calculators
Step-by-step method
- Measure the width.
- Measure the height or length perpendicular to the width.
- Multiply the two measurements.
- Attach the correct square unit to the answer.
Second example: wall 9 ft by 7.5 ft
A = w × h
A = 9 × 7.5
Result: 67.5 ft²
Practical interpretation
Rectangle area is often the first estimate for paint, flooring, wallpaper, landscaping, and sheet material. A rectangular estimate is also a good starting point for irregular spaces: divide the layout into rectangles, calculate each one separately, then add the areas together.
When measuring a room, use inside dimensions if you are estimating floor covering and wall dimensions if you are estimating paint or paneling. The same formula applies, but the measured object changes.
How to calculate this measurement
A rectangle area calculation multiplies width by height. It is one of the most common geometry calculations because it applies to rooms, screens, walls, fields, paper sizes, and rectangular materials.