A square footage calculator multiplies length by width in feet, so a room 12 ft by 14 ft covers 168 sq ft. Type each number the way your tape shows it, with feet, inches and an eighth-inch fraction if there is one. The tool converts every reading, adds or subtracts each row, and prints its arithmetic so you can check it before you order anything.
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How to measure square footage of a room
Run the tape along the floor on the longest side, wall to wall, then across the room at a right angle. Write down feet and inches exactly as the tape reads them. For a plain rectangle, those two readings are the whole job: 12 ft times 14 ft is 168 sq ft. Those 168 are squares 1 ft on each side, the unit explained in what a square foot measures.
The calculator reports that 168 sq ft room in four units at once.
| Unit | Result |
|---|---|
| Square feet | 168 sq ft |
| Square meters | 15.61 m² |
| Square yards | 18.67 sq yd |
| Acres | 0.0039 acre |
To calculate the square feet of a room with a closet, a bay or a jog in one wall, give each piece a row of its own.
Room totals suit a floor you plan to cover, but a whole house is measured around its outside walls, so its total includes the walls themselves.
Feet, inches and other units in the calculator
Divide the inches by 12, add the result to the feet, then multiply. When you calculate square footage by hand, skipping that conversion gives a wrong area. Take a kitchen that measures 15 ft 9 in by 12 ft 3 in.
Nine inches divided by 12 is 0.75, so the long side is 15.75 ft. Three inches is 0.25 ft, which makes the short side 12.25 ft. Multiply the two and you get 192.9375 sq ft, shown as 192.94.
Converted, the kitchen is 17.92 m², 21.44 sq yd or 0.0044 acre.
The slip to watch for is reading 15 ft 9 in as 15.9. Nine inches is three quarters of a foot, not nine tenths. Typed as 15.9 by 12.3, the kitchen comes out at 195.57 sq ft, 2.63 sq ft more than it really has. Separate boxes for feet and inches keep the two numbers apart, and the tool flags any inch box holding 12 or more. So 15 ft 12 in goes in as 16 ft 0 in.
For readings that fall between whole inches, the fraction picker adds anything from 1/8 in to 7/8 in. Each eighth of an inch is 1/96 ft, and the table gives every step in decimal feet.
| Fraction | Decimal feet |
|---|---|
| 1/8 in | about 0.0104 ft |
| 1/4 in | about 0.0208 ft |
| 3/8 in | 0.03125 ft |
| 1/2 in | about 0.0417 ft |
| 5/8 in | about 0.0521 ft |
| 3/4 in | 0.0625 ft |
| 7/8 in | about 0.0729 ft |
Only 3/8 in and 3/4 in end cleanly. The others repeat forever, so the calculator works at full precision and rounds only what it displays.
Square footage from meters, yards or inches
Any row of the square footage calculator can switch units. Every length still becomes decimal feet before the multiplying: yards times 3, meters divided by 0.3048, centimeters divided by 30.48. NIST, the federal National Institute of Standards and Technology, gives the international foot as 0.3048 meter exactly. Its Handbook 44 lists the inch as exactly 2.54 cm, so none of those factors is rounded. A row set to inches divides each side by 12 first, which spares you turning a square-inch total into feet by dividing by 144.
Square footage formula for each shape
A rectangle is length times width, and a triangle is half of base times height. A circle is π times the radius squared, and a trapezoid averages its two parallel sides before multiplying by the height. Each calculator row takes one of these four shapes.
| Shape | What you measure | Formula | Example |
|---|---|---|---|
| Rectangle or square | Length and width | L x W | 12 ft x 14 ft = 168 sq ft |
| Triangle | Base, and height square to the base | ½ x b x h | ½ x 10.5 ft x 8 ft = 42 sq ft |
| Circle | Diameter or radius | π x r², with r = d ÷ 2 | 5 ft 6 in across: π x 2.75 ft x 2.75 ft = 23.76 sq ft |
| Trapezoid | Two parallel sides, height between them | (a + b) ÷ 2 x h | (11 ft + 7 ft) ÷ 2 x 3.5 ft = 31.5 sq ft |
Measure a triangle or trapezoid height straight across, at a right angle to the base. A slanted side is longer than the true height, and using it inflates the area. The circle row has a toggle for diameter or radius, and π is about 3.14159.
An L-shaped room is two rectangle rows. Curved walls and outlines with many corners go faster after splitting the outline into pieces.
A wall fits a rectangle row too, width times height, and the steps for wall area cover the rest. Paint is bought against that wall figure, using the paint coverage per gallon on the label.
Square footage for multiple rooms and cutouts
Give each space its own row set to Add. Switch anything that removes floor, such as a kitchen island or a stair opening, to Subtract. A label like "Pantry" is optional, but it makes the printed lines easier to follow later.
A kitchen of 15 ft 9 in by 12 ft 3 in, plus a pantry and minus an island, totals 184.31 sq ft.
| Row | Setting | Math | Result |
|---|---|---|---|
| Kitchen | Add | 15.75 ft x 12.25 ft | 192.94 sq ft |
| Pantry | Add | 4.125 ft x 3 ft | 12.38 sq ft |
| Island | Subtract | 6 ft x 3.5 ft | 21.00 sq ft |
| Total | 192.9375 + 12.375 minus 21 | 184.31 sq ft |
The pantry is 4 ft 1 1/2 in long, and 1 1/2 in is 0.125 ft. The rounded lines add to 184.32, yet the total reads 184.31. The calculator sums the unrounded values and rounds once, at the end.
For a flooring order, type a percent into the waste box, and the tool applies it after the island comes off. At 5%, the 184.31 sq ft becomes 193.53 sq ft (184.31 x 1.05). Use the figure your own product prints, such as the 5% in Shaw Industries' engineered hardwood instructions, and how a flooring order builds in extra covers the rest.
How to read the square footage result
The total shows in square feet, with square meters, square yards and acres beside it. Square meters come from multiplying by 0.09290304, the exact factor explained in square feet to square meters. Acres come from dividing by 43,560, which the acre conversion walks through. Acres carry 4 decimals so a single room still reads 0.0039 instead of zero; the other three units carry 2.
Show the math prints one line per row, the way you would write it on paper. For the kitchen that means 15 ft 9 in = 15.75 ft, then 15.75 ft x 12.25 ft = 192.94 sq ft, then the total and the waste line.
Copy result puts those lines on your clipboard as plain text, ready to paste into a note for a supplier. Print sends the result and the lines to your browser's print dialog. Reset takes the tool back to one empty row with the waste box at 0.
A message appears next to any box that is empty, negative, or holds 12 or more inches. Everything runs in your browser, and nothing you type is sent or stored. The square footage calculator works out area only and has no price field.
Square footage of common room sizes
A 12x12 room is 144 sq ft, a 20x20 space is 400 sq ft, and a 30x40 floor is 1,200 sq ft. Each figure is length times width, and the square meters use 0.09290304 per square foot.
| Size in feet | Square feet | Square meters |
|---|---|---|
| 11 x 12 | 132 sq ft | 12.26 m² |
| 10 x 14 | 140 sq ft | 13.01 m² |
| 12 x 12 | 144 sq ft | 13.38 m² |
| 12 x 14 | 168 sq ft | 15.61 m² |
| 12 x 18 | 216 sq ft | 20.07 m² |
| 14 x 16 | 224 sq ft | 20.81 m² |
| 15 x 20 | 300 sq ft | 27.87 m² |
| 20 x 20 | 400 sq ft | 37.16 m² |
| 20 x 24 | 480 sq ft | 44.59 m² |
| 30 x 40 | 1,200 sq ft | 111.48 m² |
For a size not listed, or one with inches, type it into the calculator above, which also gives square yards and acres.
FAQ
Is square footage length times width?
Yes, for a rectangle or square, as long as both sides are in feet first. Multiplying feet by inches gives a wrong number. Triangles, circles and trapezoids use their own formulas, which is why each calculator row lets you pick the shape before you type any measurements.
Do you use height to find square feet?
Not for a floor. Floor area needs only length and width, so a room with a 9 ft ceiling and the same room with an 8 ft ceiling give one answer. Length times width times height is a volume in cubic feet, which this calculator does not work out.
How do you add square footage of two rooms?
Work out each room on its own, then add the two totals. A 168 sq ft bedroom plus a 192.94 sq ft kitchen comes to 360.94 sq ft. In the calculator, press Add area for a second row, and it sums the rooms at full precision.
Can I calculate square footage from inches only?
Yes. Set the row's unit to inches and type both sides as they read, such as 30 in by 48 in. The tool divides each by 12, giving 2.5 ft by 4 ft, or 10 sq ft. By hand, 1,440 square inches divided by 144 reaches the same 10.
How do you figure square feet without a calculator?
Turn each side into decimal feet, then multiply. Inches divided by 12 give the decimal, so 10 ft 6 in becomes 10.5 ft. Times 8 ft, that is 84 sq ft. Add any other rooms afterward, and round only the final figure so small errors do not pile up.
Does the square foot calculator round the answer?
The calculator rounds only on the screen. It works at full precision, then shows 2 decimals for square feet, square meters and square yards, and 4 for acres. So a kitchen's 192.9375 sq ft reads 192.94, while the total below it still uses the full number.
Conclusion
Before you order, hold the printed math lines up against your tape notes, because a mistyped inch is easier to spot there than in the total. Once the lines match, copy them into your note for the supplier. If a total still looks too big or too small for the space, set it beside typical room sizes and measure again.