Rectangle Area Calculator
This rectangle area calculator gives the area in square feet from a length and width in feet, inches, yards or meters (or one side, if you pick Square). You also get square yards, square meters, acres, the perimeter and the diagonal.
How to find the area of a rectangle
Multiply the length by the width, both in the same unit. Feet times feet gives square feet.
Area = length × width
- Measure both sides. For flooring, measure inside the walls; official living area under ANSI Z765 is measured outside them.
- Divide inches by 12. 13 feet 6 inches by 11 feet 3 inches is 13.5 by 11.25 feet, or use the feet and inches calculator.
- Multiply: 13.5 × 11.25 = 151.9 square feet.
- Round at the end, not before.
Common slip: 12 feet 7 inches is 12.58 feet, not 12.7.
Square inches, yards, meters and acres
The calculator converts for you, even with a different unit on each side. By hand:
14 × 6 in = 84 sq in = 0.58 sq ft. More in square inches to square feet.
144 sq ft = 16 sq yd.
A 105 × 69 m field is 7,245 m², about 77,985 sq ft.
144, 9 and 43,560 are exact (NIST Handbook 44); 10.764 is rounded from a square foot being exactly 0.09290304 m² (NIST SP 811).
Finding the length or width from the area
Divide the area by the side you know. A 57,600 square foot field that's 160 feet wide is 360 feet long.
Missing side = area ÷ known side
With only the area, many shapes fit: 200 square feet is 10 by 20 or 8 by 25. For a square, take the square root: √200 = 14.14 feet a side.
Common rectangle sizes
A 10 by 12 room is 120 square feet, a 20 by 20 two-car garage is 400, and a 50 by 120 lot is 6,000, about 0.14 acres.
Square feet and square meters of common rectangles
| Dimensions (ft) | Square feet | Square meters |
|---|---|---|
| 8 x 10 | 80 | 7.4 |
| 10 x 10 | 100 | 9.3 |
| 10 x 12 | 120 | 11.1 |
| 12 x 12 | 144 | 13.4 |
| 12 x 16 | 192 | 17.8 |
| 14 x 16 | 224 | 20.8 |
| 16 x 20 | 320 | 29.7 |
| 20 x 20 | 400 | 37.2 |
| 24 x 24 | 576 | 53.5 |
| 50 x 120 | 6,000 | 557.4 |
More sizes are on the square footage chart.
Perimeter and diagonal
Perimeter = 2 × (length + width). Diagonal = √(length² + width²).
Baseboard and fencing are bought by length (linear foot calculator). Perimeter × ceiling height is wall area for the wall calculator.
Equal diagonals mean four 90 degree corners. If they differ, length × width is only an estimate.
Squaring a corner with 3-4-5
A 3-4-5 triangle sets a right angle with just a tape, because 3² + 4² = 5².
- Mark 3 feet along one line from the corner.
- Mark 4 feet along the other line.
- Adjust until the marks are 5 feet apart. On long runs, use 6-8-10 or 9-12-15.
Concrete, paint and flooring
12 by 12 feet, 4 inches thick: 144 × 4/12 = 48 cu ft. See the concrete calculator.
20 by 9 feet (180) minus a 3 by 7 foot door (21 sq ft).
The 151.9 sq ft room above plus 10% waste. To add up several rooms, use the main calculator.
The same two measurements start the deck calculator and the countertop calculator.
When length × width doesn't work
Length × width only works with four 90 degree corners.
Split it into pieces and add them, or use the irregular shape calculator. The room calculator does L-shaped rooms; the circle square feet calculator does round patios.
Measure both lengths and both widths, average each pair, then multiply. Measuring only at the widest point inflates the area.
Frequently asked questions
How do you calculate the area of a rectangle?
Multiply length by width in the same unit. For inches, divide the result by 144 to get square feet.
How many square feet is a 12x12 room?
144 square feet. A 10 by 10 is 100 and a 15 by 15 is 225.
How do I find the width of a rectangle if I know the area?
Divide the area by the length. A rectangle of 22 square feet that's 11 feet long is 2 feet wide.
How do I find the perimeter of a rectangle?
Add the length and width, then double it. A 12 by 14 foot room is 2 × (12 + 14) = 52 feet around.
Is a square a rectangle?
Yes, one with four equal sides, so its area is one side squared. Pick Square in the calculator.