Area of a rectangle, formula and calculator.

The area of a rectangle is A = length × width. A room 8 ft long and 6 ft wide has an area of 8 × 6 = 48 square feet. The perimeter, the distance around the edge, is 2 × (8 + 6) = 28 ft. The diagonal, from corner to corner, is √(8² + 6²) = √100 = 10 ft. In other units, 48 ft² is 4.4593 m² and 5.3333 yd².

How to use the converter

1. Choose Find: the area from length and width, or a missing side from the area.
2. Type the sides, and choose a Unit of length. Use the same unit for both sides.
3. Read the big result, then The working. The cards give the perimeter, the diagonal and the area in other square units.
4. Use Copy result or Copy link to keep the answer.

Why the unit is squared

Area counts squares. A rectangle 8 ft by 6 ft holds 8 rows of 6 squares, each 1 ft by 1 ft. The answer is in square feet, written ft². To change square units, square the length factor. An inch is exactly 0.0254 m and a foot exactly 0.3048 m (NIST Special Publication 811, Appendix B.8, checked 24 Oct 2026), so a square foot is 0.3048² = 0.09290304 m², and a square yard is 9 square feet. That is why 48 ft² is 4.4593 m² and not 48 × 0.3048.

Finding a missing side

Turn the formula round: width = area ÷ length. A rectangle of 48 ft² with one side of 6 ft has another side of 48 ÷ 6 = 8 ft. Check by multiplying back. If the area is in one unit and the side in another, convert them to the same unit first.

Room sizes in feet and meters

Worked examples

• A wall 2.4 m by 3.6 m. A = 2.4 × 3.6 = 8.64 m², which is 93.00 ft².
• A sheet 297 mm by 210 mm. A = 297 × 210 = 62,370 mm², which is 623.7 cm². The factor is 100 because a cm² is 10 mm by 10 mm.
• A side from an area. A garden bed of 30 m² with one side of 4 m has the other side 30 ÷ 4 = 7.50 m.
• Mixed units. 8 ft by 72 in. Change 72 in to 6 ft first, then 8 × 6 = 48 ft². Multiplying 8 by 72 gives 576, which is not an area in any unit you meant.

The same fence, different areas

For a fixed perimeter the area changes a lot with the shape. A rope of 24 ft laid as a rectangle can enclose very different areas. The square is the best, because a square with the sides all equal gives the largest area for the perimeter: (perimeter ÷ 4)² = 36 ft².

Rooms that are not a plain rectangle

Split an L-shaped room into two rectangles and add. A room with a 5 m by 4 m main part and a 3 m by 2 m extension has 5 × 4 + 3 × 2 = 20 + 6 = 26 m². Or take a notch out of a big rectangle. A 8 m by 6 m box with a corner of 2 m by 3 m missing has 48 − 6 = 42 m². Run the tool once for each part and add the results.

Square inches to square feet

A square foot is 12 in by 12 in, so it holds 144 square inches. To change square inches to square feet, divide by 144. A panel of 96 in by 60 in has 5,760 in², and 5,760 ÷ 144 = 40 ft². Check: 96 in is 8 ft and 60 in is 5 ft, and 8 × 5 = 40. Set the unit to inches and the cards show the area in feet too.

Adding a spare allowance

If you want a spare amount of material, multiply the area by one plus the share you choose. For a floor of 4.5 m by 3.2 m the area is 14.4 m². With 10 percent spare you multiply by 1.1: 14.4 × 1.1 = 15.84 m². The 10 percent is only an example. Choose the share your supplier or plan asks for.

Check that a corner is square

The diagonal gives a quick test. If a rectangle is 6 ft by 8 ft, its diagonal must be √(36 + 64) = 10 ft. Measure both diagonals of a frame. If they are equal, and the opposite sides are equal, the frame is a true rectangle. For smaller jobs, 3 by 4 with a diagonal of 5 is the same test.

Mistakes to avoid

• Mixing perimeter and area. Perimeter adds the sides and is in feet. Area multiplies them and is in square feet. The room above has a perimeter of 28 ft and an area of 48 ft².
• Converting square units with the length factor. 1 m² is not 3.28 ft². It is 10.7639 ft², the factor squared.
• Using different units for the two sides. Convert first.
• Measuring a room that is not a rectangle. Split it into rectangles and add the areas.

For floors with several rooms see the square footage calculator. For a solid with a rectangle base, see the volume of a pyramid.