Square Footage Calculator
Last updated: October 7, 2026
Calculate area for any room shape, in square feet, square meters, or square yards.
Pick a shape, enter the dimensions, get the area. Useful for flooring estimates, paint coverage, rental listings, and renovation planning.
Room shape
How square footage is calculated
Square footage is the area of a flat surface, counted in square feet. This calculator takes dimensions in feet and uses the formula that matches the shape you pick. A rectangle is length × width. A square is side × side. A triangle is ½ × base × height, and the height has to be the perpendicular height, the straight-line distance from the base to the opposite corner measured at a right angle. A circle is π × radius × radius. The radius is half the diameter.
The result panel also converts the same area into square meters and square yards. One square yard is exactly 9 square feet, so square yards = square feet ÷ 9. Square meters = square feet × 0.09290304, which is the international foot squared (0.3048 × 0.3048). You can check a round trip: 100 square feet is about 9.29 square meters, and 9.29 ÷ 0.09290304 comes back to 100.
Irregular rooms are a sum of simple pieces. Split an L, a T, or a bay into rectangles (and a triangle if a corner is genuinely triangular), calculate each piece, and add the areas. Measure each piece in feet, including the decimal for leftover inches, before you multiply.
Worked examples
Example 1: A rectangular bedroom
Length 12 ft, width 14 ft. Area = 12 × 14 = 168 square feet. In the other units the tool reports, that is 168 × 0.09290304 = 15.61 square meters, and 168 ÷ 9 = 18.67 square yards. A flooring order for this room is not 168 by itself. Add a waste allowance after you have the net area. Ten percent extra is 168 × 1.10 = 184.8 square feet to purchase for a straight layout.
Example 2: A square patio and a circular one
A square with 10 ft sides is 10 × 10 = 100 square feet. A circle with a radius of 5 ft (a 10 ft diameter) is π × 25 ≈ 78.54 square feet. The square patio that shares the same "10" on the label is larger because the circle's corners are missing. Enter the radius for the circle, not the diameter. A 10 ft diameter entered as the radius would inflate the area by a factor of four.
Example 3: A triangular gable
Base 10 ft, perpendicular height 8 ft. Area = 0.5 × 10 × 8 = 40 square feet. If the sloping side is 9 ft, that 9 is not the height. Using it would overstate the area. Drop a tape straight down from the peak to the base, at a right angle, and use that measurement as the height.
Example 4: An L-shaped living room
The main rectangle is 20 ft by 12 ft = 240 square feet. The nook is 8 ft by 6 ft = 48 square feet. Total floor area = 288 square feet. Sketch the room and label every segment so a closet is not counted in both rectangles. Closets you will floor get their own small rectangle and are added once.
Example 5: Inches as decimal feet
Twelve feet 6 inches is 12.5 ft, because 6 ÷ 12 = 0.5. Ten feet 3 inches is 10.25 ft, because 3 ÷ 12 = 0.25. Typing 12.6 for "12 feet 6 inches" is a different length (12 feet and 0.6 of a foot, about 7.2 inches) and it will throw the area off. Convert inches first, then multiply. The Length Converter will turn a mixed length into decimal feet or into meters if a product sheet is metric.
When to use this
Flooring, tile, sod, rugs, and a check of a rental listing are floor-area jobs. So is a ceiling, which is usually the same rectangle as the floor if the room is a simple box. Paint on the walls is a different surface: perimeter × ceiling height, minus doors and windows. A 12 by 14 ft room with 9 ft ceilings has 168 square feet of floor and about 468 square feet of wall before openings. Use the Paint Coverage Calculator for that wall estimate. For turf, the Sod Calculator starts from area and helps with piece counts. For a slab, area is only the footprint; thickness turns it into volume in the Concrete Volume Calculator.
Listings and appraisals often mean "finished living area," which may exclude the garage, an unfinished basement, or open porches. Measure the surface you are actually covering. If you are comparing two apartments, use the same definition for both so a 900 square foot unit with a large balcony is not treated as identical to 900 square feet of interior floor.
Common mistakes
- Feet-and-inches typed as one decimal. 8 ft 11 in is 8 + 11/12 = 8.9167 ft, not 8.11.
- Diameter used as the radius. The circle field asks for the radius. Half the width of the circle is the number to type.
- Slant used as triangle height. Only the perpendicular height belongs in the formula.
- Linear feet treated as square feet. Baseboard and fence length are length, not area. A 40 ft wall is not 40 square feet.
- Waste forgotten, or applied twice. Compute net area, then add one waste percent for the whole job.
- Cabinets and islands. Flooring usually runs under the cabinets you will not install yourself, and stops at a permanent island only if the plan says so. Decide before you order.
Limitations
The inputs are feet. Metric plans need a conversion to feet first, or you can multiply length and width in meters yourself and treat the answer as square meters. The tool does not apply a waste factor, does not subtract islands, and does not price the material. It is flat area, so a sloped ceiling or a stair run needs a separate measurement along the slope. It does not compute volume and it does not compute board feet of lumber. Very large results are still just the product of the dimensions you typed; a misplaced extra zero on the length will look like a warehouse.
FAQ
How many square feet are in an acre?
An acre is 43,560 square feet. A quarter acre is 10,890 square feet. Lot size in acres is land area, which is a different measurement from the heated floor area of the house sitting on it.
Can I enter meters?
The dimension fields are in feet. Convert each side with the length converter, or calculate in meters and skip this tool's square-foot line. The square-meter figure on the panel is a conversion of a square-foot result, not a place to type meters directly.
How much extra flooring should I buy?
A common allowance is about 5% to 10% for a straight lay of plank or tile, and about 10% to 15% for a diagonal layout, a pattern, or a lot of cuts. Add that percent to the net area. Keep a few extra planks for later repairs if the dye lot may disappear.
Why is my wall area so much larger than the floor?
Walls wrap the room and rise to the ceiling. Perimeter times height counts four walls. The floor only counts the footprint. Subtract doors at about 21 square feet each and ordinary windows at about 15 square feet each, or measure the openings you actually have.
Do square feet and square yards use the same dimensions?
Yes. Enter feet, read both. Because a yard is 3 feet, a square yard is 3 × 3 = 9 square feet. Carpet is often sold by the square yard; divide the square-foot result by 9.
Practical tips
Measure to the nearest inch, convert to decimal feet, and write the decimals on a sketch before you calculate. Measure the length in two places on an old house; if the walls are not parallel, use the average or split the floor into two triangles. For tile, confirm whether the box coverage already includes a waste recommendation. For sod, measure the planting beds you will not cover and subtract them so you do not buy turf for the mulch.
If a product is priced per square foot, multiply that price by the area you will purchase, waste included, and then compare suppliers with the unit price calculator. A cheaper price per square foot on a material that needs 15% waste can lose to a slightly higher price with less waste.
Record the unit next to every number you copy into a quote. Mixing one side in inches and the other in feet is the error that produces a room "bigger than the lot." The calculator will multiply whatever feet you give it.