Square Footage Calculator
Measure the square footage of rectangles, L-shapes, circles, triangles and trapezoids, with cut-outs and waste. Free, no sign-up, and it runs in your browser.
Dedicated page: /en/square-footage-calculator
Add up to 4 areas. Each area can add to the total or subtract from it, for cut-outs like a kitchen island or a closet you are not covering. Enter dimensions in decimal feet: 12 ft 6 in is 12.5 ft. Use the converter below if you measured in feet and inches.
Feet and inches to decimal feet
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Quick answer
A square footage calculator works out the area of a room or space in square feet. Enter the dimensions for rectangles, L-shapes, circles, triangles or trapezoids, add several areas together, subtract cut-outs like islands and closets, and it returns the total in square feet, square yards, square metres and acres, with a waste allowance for buying materials.
About this Square Footage Calculator
Measure the square footage of rectangles, L-shapes, circles, triangles and trapezoids, with cut-outs and waste. It is one of the Home and DIY on ToolUstad, and like every tool here it runs entirely in your browser: nothing you type, paste or open is uploaded to a server, and there is no sign-up or usage limit.
What is a square footage calculator?
Square footage is length times width, with both measurements in feet. A room 20 ft by 14 ft is 280 square feet. That is the whole formula for a rectangle, and everything else on this page is about handling measurements that are not clean feet, shapes that are not rectangles, and rooms that are not one simple box. The calculator takes up to four areas, adds or subtracts them, converts the total, and adds a waste allowance.
The five shapes cover almost everything you will measure. A rectangle is length times width. A circle is pi times the radius squared. A triangle is half the base times the perpendicular height. A trapezoid is half the sum of the two parallel sides times the height. An L-shape is the outer rectangle minus the cut-out rectangle, which is how you measure a room with an alcove or a missing corner.
Feet and inches, and the mistakes they cause
Most manual errors come from inches. Rooms are rarely whole feet, and you cannot multiply feet by inches directly. Convert the inches to a decimal fraction of a foot first by dividing by 12: 6 inches is 0.5 ft, 7 inches is 0.583 ft, 9 inches is 0.75 ft. A room measuring 12 ft 7 in by 10 ft 4 in is 12.583 ft by 10.333 ft, which is 130 sq ft. Doing it wrong, multiplying 12.7 by 10.4, gives 132 sq ft.
Two more mix-ups cost people money. A square yard is 9 square feet, not 3, because area scales with the square. And for a triangle, height means the perpendicular distance from the base to the opposite point, not the length of a sloping side.
Waste, cost and whole-house figures
Waste is not guesswork: it depends on the material and the pattern. Straight-lay plank flooring and tile need 10 percent, diagonal tile or plank 15 percent, herringbone or chevron 15 to 20 percent, carpet 10 to 20 percent because roll width forces seam placement, and paint needs none, since you round up to the next can instead. On 424 sq ft with 10 percent waste, buy 466.4 sq ft. At $3 per sq ft, that is $1,399.20.
Room totals are not house square footage. Listings and appraisals use the ANSI Z765 standard, which measures finished living area from the exterior face of exterior walls and excludes garages, unfinished basements and attics, and open porches. Measuring each room from the inside and adding them comes out lower, typically by 5 to 10 percent, because interior measurements exclude wall thickness, hallways and stair openings.
Best practices
- Measure each wall twice: rooms are rarely truly square, so check the width at both ends and use the larger figure for ordering.
Common mistakes to avoid
- Treating 12 ft 7 in as 12.7 ft. Seven inches is 0.583 ft, not 0.7.
- Confusing square yards with square feet: a square yard is 9 square feet.
- Ordering the exact area with no waste, then running short on the last row of flooring.
Who is the square footage calculator for?
Homeowners measuring rooms for flooring, paint, tile or carpet, renters checking a listing figure, and DIY builders working out material quantities.
Learn: how to use the Square Footage Calculator
- Pick a shape for area 1 and enter its dimensions in decimal feet. 12 ft 6 in is 12.5 ft, and the converter below does the maths.
- Add up to three more areas, and set each one to add to the total or subtract as a cut-out.
- Pick a waste allowance for the material you are buying, and a price per square foot if you want a cost.
- Read the total in square feet, square yards, square metres and acres, plus the area to buy with waste.
- Use the perimeter figure for baseboard, and the table to check each area.
Features
- Five shapes: rectangle, L-shape, circle, triangle and trapezoid
- Up to 4 areas, each one added or subtracted for cut-outs
- Feet and inches converter to decimal feet
- Waste allowance at 0%, 10%, 15% or 20% with the buy quantity
- Conversions to square yards, square metres and acres
- Cost estimate from your price per square foot, and a downloadable worksheet
Worked example
A 20 by 14 ft living room is 280 sq ft and a 12 by 12 ft bedroom is 144 sq ft, 424 sq ft together. That is 47.1 sq yd, 39.4 sq m and 0.0097 acres. With 10% waste for straight-lay flooring, buy 466.4 sq ft. At $3 per sq ft the flooring costs $1,399.20. The two rooms have a combined perimeter of 116 ft for baseboard.
Frequently asked questions
How do I calculate square footage?
Multiply length by width, both in feet. A 20 ft by 14 ft room is 280 square feet.
How many square feet is a 12 x 12 room?
144 square feet. That is 13.4 square metres or 16 square yards, with a perimeter of 48 feet for baseboard. At 10% waste you would buy flooring for about 158 square feet.
How do I measure an irregular room?
Break it into rectangles, triangles and circles, measure each separately, and add them. Subtract any cut-outs such as islands or closets you are not covering. This calculator lets you enter multiple areas and set each one to add or subtract.
How many square feet are in a square yard?
Nine. A square yard is 3 ft by 3 ft, so the area scales by 3 times 3. Carpet is commonly priced by the square yard, which is why the mix-up costs people money.
How many square feet are in an acre?
43,560 square feet. An acre was historically one chain by one furlong, 66 ft by 660 ft. It is roughly 4,047 square metres or 0.405 hectares.
How is house square footage measured?
US residential listings commonly follow ANSI Z765, which measures finished living area from the exterior face of exterior walls and excludes garages, unfinished basements and open porches.
How much extra flooring should I buy?
10% for straight-lay planks or tile, 15% for diagonal patterns and large-format tile, and 15 to 20% for herringbone or chevron.
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