Square footage calculator, add rooms, take away cut-outs.

To find square footage, multiply the length of a space by its width, with both in feet. A room 12 ft long and 15 ft wide is 12 × 15 = 180 square feet. This square footage calculator does that sum for rectangles, L shapes, triangles, trapezoids and circles, adds the pieces of a floor plan together, takes cut-outs away, and shows the total in square feet, square yards, square metres and acres.

How to use the square footage calculator

1. Pick the Shape: "Rectangle or square", "L shape", "Triangle: base and height", "Triangle: three sides", "Trapezoid", "Circle", or "An area I already know".
2. Pick the Unit. Feet, inches, yards, metres and centimetres all work, and the answer is always shown in square feet as well.
3. Type the sizes. You can type 12.5, a fraction like 3 1/2, or feet and inches like 12'6". The page reads 12'6" as 12 feet 6 inches whatever Unit is picked.
4. Type "How many of them" if you have several of the same piece, such as four equal bedrooms.
5. Choose what "This piece will" do: "Add" to the total, or "Take away" (a cut-out).
6. Give it a Name if you like, then press "Add to the list" or press Enter. The pieces show in the list with a drawing of each one, all at the same scale.
7. Press the plus or minus sign in the list to switch a piece between adding and taking away. Press the cross to remove it.
8. To see extra for waste, type a percent in "Extra for waste (%)" or press 5, 10 or 15. To see the cost, type the "Price per sq ft" from your quote.
9. Use "Copy the list", "Print" or "Copy link" to keep the work. The link carries the whole list.

Worked example: two rooms minus a closet

• Living room 12 ft × 15 ft: 12 × 15 = 180 sq ft.
• Bedroom 10 ft × 12 ft: 10 × 12 = 120 sq ft.
• Closet 2 ft × 4 ft, taken away: 2 × 4 = 8 sq ft.
• Total: 180 + 120 − 8 = 292 sq ft. That is 292 ÷ 9 = 32.44 sq yd, 292 × 0.09290304 = 27.13 sq m, and 0.0067 acres.
• With 10% waste: 292 × 1.10 = 321.2 sq ft. If you type a price of 3 a square foot, the cost is 321.2 × 3 = 963.60.

L shapes, triangles, trapezoids and circles

An L shape is a big rectangle with a corner missing. Type the overall length and width, then the size of the missing corner. A shape 20 ft by 14 ft with an 8 ft by 6 ft corner missing is 20 × 14 − 8 × 6 = 280 − 48 = 232 sq ft. A triangle is half of base times height: a gable end 24 ft wide and 8 ft tall is 24 × 8 ÷ 2 = 96 sq ft. If you only know the three sides, the page uses Heron's formula: sides 13, 14 and 15 give a half-perimeter of 21 and an area of the square root of 21 × 8 × 7 × 6, which is 84. A trapezoid has two parallel sides: the average of the two, times the height. Sides of 10 and 14 with a height of 8 give 12 × 8 = 96 sq ft. A circle is π × radius × radius: a round patio 10 ft across has a radius of 5, so the area is 3.1416 × 25 = 78.54 sq ft.

Units and conversions

The conversions are exact definitions: 1 ft = 0.3048 m, 1 in = 2.54 cm and 1 yd = 0.9144 m (NIST Special Publication 811, Appendix B.8, checked 18 Oct 2026). So 1 sq ft is exactly 0.09290304 sq m. This page uses 43,560 sq ft for an acre. NIST lists the acre based on the US survey foot as 4,046.873 sq m, which differs from this page's value by about four parts in a million.

A room measured as 3 m by 4 m is 12 sq m, which is 12 ÷ 0.09290304 = 129.17 sq ft. To convert other units, the unit converter has an Area group.

Waste and cost

Waste is the extra you buy to cover cuts, patterns and mistakes. The calculator starts at 0 and adds whatever percent you type, since the right margin depends on the material and the layout. Ask your installer, or read the product's own guidance. The cost is the area with waste times the price a square foot that you type. No prices are built in. Treat it as maths for planning, not a quote.

Common problems

• Irregular rooms. Split them into rectangles and triangles, add each piece, and check the pieces do not overlap.
• Mixed units. Pick one Unit for a piece. To mix, type feet and inches like 8'4" and the page does the rest.
• A cut-out bigger than the room. If the total goes negative, a piece is marked "Take away" by mistake. Press its minus sign to flip it.
• Walls are not floor. This page finds flat area. For paint on walls, work out each wall as a rectangle and take away the doors and windows.

For volume jobs, such as a slab on that floor area, the concrete calculator turns length, width and depth into cubic yards. To find a percent of an area, like 15% waste on its own, use the percentage calculator.