Square footage calculator for rooms, floors and lots
A 12 by 10 ft room is 120 square feet, 13.3 square yards or 11.1 square meters. Type each room in feet and inches as you measured it, and take out the closet or the hearth. The total comes with the waste allowance and the box count for flooring.
Area formulas the calculator uses
Every shape comes down to a handful of formulas, all worked in feet before the result is converted. A rectangle is length times width. A circle is pi times the radius squared, where the radius is half the diameter you measured across the widest point. A triangle is half the base times the height. When you only have the three sides, it is Heron's formula. With s as half the perimeter, the area is the square root of s(s − a)(s − b)(s − c). A trapezoid is the average of its two parallel sides times the distance between them. An oval is pi times half its length times half its width. An L-shape is the full rectangle minus the missing corner, and a ring is the outer circle minus the inner one.
Rectangle: length × width. Circle: 3.1416 × (diameter ÷ 2)². Triangle: base × height ÷ 2. Trapezoid: (side a + side b) ÷ 2 × height. Square yards: square feet ÷ 9. Square meters: square feet × 0.0929.
Inches are converted first, so 10 ft 6 in is 10.5 ft, not 10.6. That single step is where most hand calculations go wrong. How to calculate square footage works through each shape by hand.
Common room sizes in square feet, square yards and square meters
| Room | Size | Square feet | Square yards | Square meters |
|---|---|---|---|---|
| Small bedroom | 10 × 10 ft | 100 | 11.1 | 9.3 |
| Bedroom | 12 × 12 ft | 144 | 16.0 | 13.4 |
| Kitchen | 10 × 12 ft | 120 | 13.3 | 11.1 |
| Living room | 16 × 20 ft | 320 | 35.6 | 29.7 |
| Primary bedroom | 14 × 16 ft | 224 | 24.9 | 20.8 |
| Full bathroom | 8 × 10 ft | 80 | 8.9 | 7.4 |
| Two-car garage | 20 × 22 ft | 440 | 48.9 | 40.9 |
| Patio | 10 × 14 ft | 140 | 15.6 | 13.0 |
Use these to sanity-check a measurement: a bedroom called 12 by 12 that comes out far from 144 square feet usually has inches typed into a feet box.
Three rooms of flooring, one closet taken out
A hallway 3 ft 6 in by 14 ft is 49 square feet. The bedroom off it is 12 ft 3 in by 11 ft 9 in, which is 143.9 square feet. Its closet, 2 ft by 6 ft, is 12 square feet that will get a different floor, so it comes out. The living room is an L: 20 by 15 ft is 300 square feet. Take away the 6 by 5 ft corner the kitchen takes, and that leaves 270 square feet. The total is 49 + 143.9 − 12 + 270 = 450.9 square feet. Laid straight with 10% extra, that is 496 square feet to buy. In boxes of 22.5 square feet it is 23 boxes, with about one box left over for repairs.
Measuring so the number is right the first time
Measure at floor level along the longest part of each wall, because walls bow and rooms are rarely square. Take the width in two places and use the larger one when you are buying material. Measure doorways to the far side of the threshold if the new floor will run through them. For a lot or a yard, pace it off first, then measure with a long tape or a wheel. The calculator accepts an area you already know, so a plat or a county record figure can go straight in. For walls, measure the perimeter once at the baseboard and multiply by the height instead of measuring each wall's face.
The waste allowances the calculator offers
| Layout | Option |
|---|---|
| Plank or tile laid straight in a simple room | 5% |
| Laminate or vinyl plank, the usual flooring allowance | 10% |
| Tile or plank laid diagonally or in a herringbone pattern | 15% |
| Rooms with many angles, bay windows, curves | 20% |
These are the choices in the options box, not a rule. Flooring makers print their own allowance on the box or in the installation guide, and when they do, theirs wins. Carpet is the exception to area math altogether, because it comes in 12 ft wide rolls. So a 13 ft wide room needs a seam and more material than its square footage suggests. Ask the installer for the cut plan before ordering.
Questions about measuring square footage
How do I calculate the square footage of a room?
Measure the length and the width in feet and inches, turn the inches into a decimal (divide by 12), and multiply the two. A room 12 ft 6 in by 10 ft 3 in is 12.5 × 10.25 = 128.1 square feet. The calculator does the inch conversion for you, so type 12 and 6 in the two boxes.
How do I measure an L-shaped or odd room?
Split it into rectangles, measure each one, and add them. For an L, measure the full outside length and width, then measure the missing corner and take it away. The L-shape option does exactly that. Triangles, circles and trapezoids have their own options. A bay window or a curved wall is usually close enough as a trapezoid or a half circle.
How many square feet is a 12x12 room?
A 12 by 12 room is 144 square feet, which is 16 square yards or 13.4 square meters. With the usual 10% extra for cuts, buy flooring for about 158 square feet. In boxes that cover 20 square feet each, that is 8 boxes.
How much extra flooring should I buy?
The allowance printed on the box or in the maker's installation guide, which is the figure the options box is there to hold. The presets run from 5% for planks laid straight in a simple room to 20% for a room with many angles or a herringbone pattern. Buy whole boxes and keep one unopened box for repairs.
How many square feet are in a square yard, a square meter and an acre?
A square yard is 9 square feet, a square meter is 10.764 square feet, and an acre is 43,560 square feet. Carpet is often quoted by the square yard, so a 12 by 15 ft room (180 sq ft) is 20 square yards of carpet.
What counts in a house's square footage?
US listings and appraisals follow the ANSI Z765 method, which Fannie Mae requires of appraisers; the figures here are from the standard's 2021 public-comment draft. Finished areas are measured at floor level to the outside face of the exterior walls, with ceilings of at least 7 ft. They are reported to the nearest whole square foot, with above-grade and below-grade areas reported separately. Garages and unfinished areas are left out. Measuring room by room from the inside gives a smaller number, by about the thickness of the walls.
How do I work out the wall area for paint?
Add the lengths of the walls to get the perimeter, multiply by the ceiling height, then take out the doors and windows. A 12 by 10 ft room with 8 ft ceilings has 44 ft of wall, so 352 square feet. A 3 by 7 ft door is 21 square feet. A 3 by 4 ft window is 12, so with one door and two windows there are about 307 square feet to paint. Enter the walls as rectangles here and tick the doors and windows as areas to take away. Then divide by the coverage printed on the paint can.
2 source documents
- Home Innovation Research Labs, secretariat of ANSI Z765, Square Footage, Method for Calculating: ANSI Z765 public-comment draft of the 2021 edition (measuring to the exterior face of the walls, 7 ft ceilings, reporting rules), draft; the published Z765-2021 is sold by Home Innovation. Read 2 November 2026.
- Home Innovation Research Labs, Square Footage Method, frequently asked questions (Fannie Mae requires ANSI Z765-2021 for appraisers; garages and unfinished areas excluded). Read 2 November 2026.