Square footage calculator for L-shaped and irregular rooms
Break the room into simple shapes, add the ones that are floor, subtract the ones that are not, and get the total in square feet, square metres and square yards.
Total area
222.0 sq ft
20.62 m² · 24.67 sq yd
2 shapes adding 228.0 sq ft (21.18 m²), less 6.00 sq ft (0.557 m²) taken out.
Shape by shape
| Shape | Size | Area |
|---|---|---|
| 1. Rectangle | 15 ft (4.57 m) × 12 ft (3.66 m) | + 180.0 sq ft (16.72 m²) |
| 2. Rectangle | 8 ft (2.44 m) × 6 ft (1.83 m) | + 48.0 sq ft (4.46 m²) |
| 3. Rectangle | 3 ft (0.91 m) × 2 ft (0.61 m) | − 6.00 sq ft (0.557 m²) |
How to use it
Sketch the room on paper first. Draw straight lines that divide it into rectangles, with a triangle for any angled wall and part of a circle for a curved bay. Measure each piece, enter it as a shape, and set it to add. Then enter anything inside those shapes that is not being covered (a fireplace hearth, a built-in cupboard, a kitchen island you are not flooring under) and set it to subtract.
The shapes must not overlap, or the overlap is counted twice. Rows you leave empty are ignored. Imperial dimensions take feet as decimals (12.5) or feet and inches (12' 6"); metric takes metres.
The formulas
- Rectangle: length × width.
- Triangle: ½ × base × height, where the height is measured at right angles to the base. For a right-angled corner cut off a room, the base and height are the two short sides.
- Half circle: π × diameter² ÷ 8. A semicircular bay measured straight across its opening.
- Quarter circle: π × radius² ÷ 4. A rounded corner, measured from the corner point out along either wall.
Totals are converted with exact factors: 1 sq ft = 0.09290304 m², and 1 sq yd = 9 sq ft = 0.83612736 m².
A worked example
The default is an L-shaped living and dining room. The main part is 15 × 12 ft, which is 180 sq ft. The dining nook off one side is 8 × 6 ft, another 48 sq ft. A 3 × 2 ft built-in cupboard in the corner is not being floored, so 6 sq ft comes off. The total is 180 + 48 − 6 = 222 sq ft, which is 20.62 m² or 24.67 sq yd.
Notice what measuring the bounding rectangle would have given: if the whole L sits inside a 23 × 12 ft box, that is 276 sq ft, 24% more than the real floor. That is the most common way flooring gets over-ordered.
Splitting common room shapes
- L-shape: two rectangles. Or one big rectangle, minus the missing corner as a subtracted rectangle.
- T-shape or U-shape: three rectangles.
- Room with one angled corner: the full rectangle, minus a triangle for the corner that is cut off.
- Bay window: the main rectangle, plus a rectangle and two triangles for a canted bay, or a half circle for a round one.
- Hallway with doorways: the hall as one rectangle; the floor in each doorway to the threshold as a small rectangle each.
Where this stops being reliable
- Rooms that are not square. Rectangles assume right-angled corners. In an old house where opposite walls differ by more than an inch or two, measure both and use the average, or split the room into a rectangle and a thin triangle.
- Irregular curves. A curve that is not a true circular arc is only approximated. Split it into several narrow triangles or rectangles for a better figure.
- Area is not the order quantity. Flooring, tile and carpet all need a waste allowance on top, and carpet comes in fixed roll widths that can add far more. Take this area into the flooring calculator or the floor tile calculator.
Common questions
How do I find the square footage of an L-shaped room?
Split it into two rectangles with one straight line, measure each, multiply length by width for each and add them. It does not matter which way you split it as long as the two pieces do not overlap. The alternative, which gives the same answer, is to measure the bounding rectangle and subtract the missing corner.
How do I convert square feet to square metres or square yards?
One square foot is exactly 0.09290304 m², so multiply square feet by 0.0929, or divide square metres by 0.0929 (roughly, multiply by 10.764). A square yard is 9 square feet, which is how carpet is often priced in the US; divide square feet by 9.
Should I measure to the wall or to the baseboard?
To the wall, at floor level, for flooring. Baseboard is normally removed or goes on after the floor, and the floor runs under where it sits. For paint or wall area the question is different; measure the walls themselves.
How do I measure a room with an angled wall?
Square off the room with a rectangle that stops where the angle begins, then treat the angled part as a right-angled triangle: its base is the length along the square wall, and its height is the distance at right angles out to the far corner. Area is half base times height. For a wall that is angled at both ends, a rectangle and two triangles, or one trapezoid split into those, will do it.
How accurate does my measuring need to be?
To the nearest inch or centimetre is plenty for ordering flooring, because you add a waste allowance of 5 to 20% anyway. An error of one inch in each direction of a 12 × 15 ft room changes the area by about 2 sq ft, around 1%. It matters more for cutting than for ordering.
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