Square footage calculator
Calculate area in square feet, square yards, and square metres. Works with feet and inches, decimal feet, inches, or millimetres. Handles rectangles, triangles, circles, trapezoids, and irregular polygons with a running total.
Your area
156.25 sq ft
For flooring, add 10% for a straight lay and 15% for a diagonal, then round up to whole boxes. The app does area and volume too, and works with no signal.
A = length × width
Use this square footage calculator to find the area of a room, floor, wall or odd shape in square feet, square yards and square metres. Enter the length and width in feet and inches with fractions, decimal feet, plain inches or millimetres. It converts both measurements to inches, multiplies without rounding first, and gives the area in all three units.
Room square footage calculator
A room is length by width. The common mistake is multiplying the feet by the feet and the inches by the inches, then adding the two: for a 12 ft 6 in square room that gives 144 + 36 = 180, when the correct area is 156.25 sq ft. Type 12' 6-1/2" straight in and let the calculator do the conversion: it takes both measurements to inches, multiplies there, and divides by 144 at the end.
Square footage from inches
If your measurements are already in inches, multiply the two inch figures and divide by 144. A 150 in by 150 in room is 22,500 square inches, which is 156.25 sq ft. The calculator handles this automatically — just type 150" into any field.
Square footage for flooring
Find the floor area first, then add waste: 10% for a straight lay, 15% for a diagonal or herringbone pattern. Round up to whole boxes. Buy the extra material in the same dye lot as the main order — a box bought later will not match. This calculator gives you the base area. Add the waste and round up to whole boxes yourself.
Slab and patio square footage
A slab is measured by area first, then multiplied by depth for the volume. For a 20 ft by 30 ft slab the area is 600 sq ft, and at 4 in deep that is 200 cu ft, or about 7.4 cubic yards. To check that the forms are square before a pour, compare the two diagonals with the diagonal calculator. For bags, waste and ready-mix orders, see the RawMath concrete calculator.
Wall square footage calculator for paint
Length times height for each wall, added together, minus the openings. Use the running total above: add each wall as its own area, then subtract each window and door. One gallon of paint covers roughly 350 to 400 sq ft on a smooth surface, less on textured.
Triangle, circle, trapezoid, and irregular shapes
Switch the shape chip to TRIANGLE (base × height ÷ 2), CIRCLE (πr², using the diameter you enter), or TRAPEZOID (average of the parallel sides × the height). For a room or plot that is not a regular shape, switch to IRREGULAR and enter each corner as x,y coordinates in feet, going round in one direction. The calculator uses the shoelace formula — the same method a surveyor uses — and it is exact for any polygon that does not cross itself.
Questions about square footage
How do you calculate square footage with feet and inches?
Convert both measurements to inches, multiply, then divide by 144. A 12 ft 6 in by 10 ft 3 in room is 150 in × 123 in = 18,450 square inches, which is 128.125 sq ft. Multiplying the feet by the feet and the inches by the inches and adding the two gives the wrong answer.
How do I work out square footage from inches?
Multiply the two inch figures and divide by 144, because there are 144 square inches in a square foot. A 150 in by 150 in room is 22,500 in², which is 156.25 sq ft.
How do you find the square footage of an irregular room?
Split it into rectangles and add them with the running total, or switch to IRREGULAR and walk the corners as x,y coordinates going round in one direction. The second way uses the shoelace formula and handles any shape that does not cross itself.
How many square feet is a 12×12 room?
144 sq ft, if both 12s are feet. A 12 ft 6 in square room is 156.25 sq ft, which is what six inches on each side is worth.
How do I calculate square footage for flooring?
Work out the floor area, add 10% for a straight lay or 15% for a diagonal or a herringbone, then round up to whole boxes. Buy the waste in the same dye lot as the rest; a box bought six months later will not match.
How do you calculate the square footage of a wall for paint?
Length times height for each wall, added together, then subtract each door and window as its own area. Use the running total for that: add the walls, then subtract the openings. One gallon covers roughly 350 to 400 sq ft on a smooth surface, less on texture.
How many square feet are in a square yard?
Nine. A square yard is three feet by three feet. Carpet and some concrete work are priced by the yard, which is why the conversion sits in the results above.
How do I convert square feet to square metres?
Multiply by 0.09290304. A 156.25 sq ft room is 14.52 m². The conversion is exact, because a foot is defined as exactly 0.3048 m.
How do I calculate concrete square footage for a slab?
Find the slab area the same way — length times width — then multiply by the slab depth to get cubic volume. A 20 ft by 30 ft slab is 600 sq ft; at 4 in deep that is 200 cu ft, or about 7.4 cubic yards.
