Square footage calculator: how many square feet do I have?
Rooms, L-shapes, circles and triangles in feet and inches or meters. Free, no sign-up, nothing leaves your browser.
How the square footage calculator works
You type each length the way the tape gave it to you, and the calculator shows its reading right under the field. 12' 6" reads as 12.5 ft. 10.10 reads as 10 ft 1.2 in, and that's the one to watch. On a phone calculator it looks like ten foot ten, and in a 12-foot room the difference is about 9 square feet.
Every shape has its own formula, filled in with your numbers. A rectangle is length times width. An L-shaped room is the full box, wall A times wall B, less the corner that isn't there, wall C times wall D. A circle starts from the diameter, because that's what a tape gives you across a round patio, and the calculator halves it for you. A triangle takes a base and a height square to it, or all three sides.
Cut-outs come off the shape they sit in, so an island never gets subtracted from the bedroom. Each area is rounded half-up to two decimals, and the total adds the areas as shown, so a phone calculator gets the same total. Square meters use the international foot, exactly 0.3048 m. NIST retired the old US survey foot at the end of 2022 and keeps it only for historic and legacy work. A square yard is 9 square feet.
Type a price and the cost line is area times your price. It adds nothing for waste, labor or tax.
Who this is for
You're pricing a floor, ordering sod, checking whether a rug fits, or adding up rooms to set beside a listing. You have a tape or a floor plan and you want one number you can stand behind.
This calculator stops at area. Tiles and boxes live on the tile calculator, wall sheets on the drywall calculator, boards and posts on the deck and fence calculator, gravel and mulch by the cubic yard on the landscaping material calculator, and a roof's real surface on the roofing calculator.
Homeowner questions about square footage
How do you calculate the square footage of a room?
Multiply the length by the width, both in feet. A room 12 ft 6 in by 11 ft 3 in is 12.5 times 11.25, or 140.63 square feet. Measure wall to wall at floor level, and measure both long walls, because rooms are rarely square. If they differ, we'd buy for the longer one. A closet or a bump-out you're covering goes in as its own rectangle.
How do I calculate square footage with feet and inches?
Divide the inches by 12 to turn them into feet, then multiply. Six inches is 0.5 ft, three inches is 0.25 ft. The trap is the decimal point: 10.10 is ten and one-tenth feet, which is 10 ft 1.2 in, not 10 ft 10 in. Type 10' 10" here and the calculator does the dividing.
How many square feet is a 12x12 room?
144 square feet, as long as both walls really measure 12 ft. Make one of them 12 ft 6 in and you're at 150. Six square feet is the size of the gap between a guess and a tape.
How do I find the square footage of an L-shaped room?
Take the full box and subtract the missing corner. Measure the two long outside walls, then the two short walls at the inside corner. A 24 ft 6 in by 18 ft box missing a 10 ft 6 in by 7 ft corner is 441 minus 73.5, or 367.50 square feet. Splitting it into two rectangles works too, unless both run to the far walls. Then the overlap counts twice, and the same room comes out at 521.50.
How do you find the square footage of a circle from the diameter?
Halve the diameter to get the radius, then multiply pi by the radius times itself. A round patio 10 ft across has a 5 ft radius: 3.14159 times 25 is 78.54 square feet. Use 5 ft as if it were the diameter and you get 19.63, a quarter of the real answer. That's why the calculator asks for the diameter and shows you the radius.
How do I find the square footage of a triangle with 3 sides?
Use Heron's formula. Add the three sides, halve the sum and call that s. Multiply s by s minus each side, then take the square root. Sides of 13, 14 and 15 ft give s = 21, and the root of 21 times 8 times 7 times 6 is 84 square feet. If you have a base and a height square to it, skip all that: it's half of base times height.
Does square footage include closets?
For a floor you're covering, yes, if the flooring runs into the closet: add it as its own rectangle. A home's official square footage is a different question. That one is answered by an appraiser's standard, not by adding up rooms.
Why doesn't my total match the listing's square footage?
Because a house is measured differently from the floors inside it. Fannie Mae requires ANSI Z765-2021 for single-family hybrid appraisals and appraisals requiring interior and exterior inspections. A different state or regulatory standard can apply. ANSI's publisher says it "does not cover room dimensions". Apartment units in condo or co-op buildings use "interior perimeter measurements". We can't tell you how a particular listing got its number. Your total here is the floor of the shapes you typed.
How many square feet are in a square yard?
Nine: a square yard is 3 ft by 3 ft. If a quote comes per square yard, divide it by 9 to get the price per square foot, so $24.84 a yard is $2.76 a foot. Type a price here and the calculator shows it both ways. That's how you catch a per-yard figure sitting in the per-foot box.
How to calculate square footage of a room
Sketch the floor first, even badly. Then break it into shapes you can measure: the main rectangle, the bump-out, the closet, the bay. An angled wall makes a triangle, so measure its three sides. A round patio is a circle. Measure straight across it, through the middle.
Measure at floor level, wall to wall, and write feet and inches the way the tape shows them. Then take out what the floor won't cover: an island, a hearth, a tub base, a column. Doors and windows don't come off a floor at all. They're a wall question, and the drywall calculator handles them.
Do this once per room and the arithmetic stops being the hard part. The hard part is remembering which wall was 11 ft 3 in, so write it on the sketch as you go.
Sources and last checked
- Length and area definitions: NIST Handbook 44 (2026), Appendix C, General Tables of Units of Measurement. 1 ft = 0.3048 m exactly; 1 in = 2.54 cm exactly; 1 sq yd = 9 sq ft; 1 sq ft = 0.09290304 sq m.
- Which measuring standard Fannie Mae asks appraisers to use on a single-family home: Fannie Mae Selling Guide B4-1.3-05, Improvements Section of the Appraisal Report (Guide published October 7, 2026).
- What ANSI Z765 covers: Home Innovation Research Labs, Square Footage Method FAQ.
Last checked: October 8, 2026 (unit definitions version remains 2026-10-07).
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