How do I calculate the square footage of an L-shaped room?

Split it into two rectangles with one straight line, measure each rectangle separately, and add the two areas. Measure the second rectangle as it exists after the split, not as a whole-building dimension, or you will double-count the overlap.

How many square feet are in a square yard?

Nine. A square yard is three feet by three feet. To convert square feet to square yards, divide by 9 — a 300 sq ft room is 33.3 sq yd. Carpet is still commonly quoted this way.

What is a 'square' in construction?

One square is 100 square feet. Roofing and siding are both ordered in squares, so a 2,400 sq ft roof is 24 squares. It is not a square that is one unit on a side, and mixing it up by a factor of 100 is a costly mistake.

How much waste should I add?

Ten percent for straight-lay flooring and tile in a simple rectangular room. Fifteen percent for diagonal or herringbone patterns, small cut-up rooms, or large-format tile. Zero if you only want the true measured area.

Do I include closets and doorways?

Include them if the finished surface continues into them, which for flooring it usually does. Exclude built-in cabinetry, kitchen islands and hearths that are staying put. When in doubt include it — the extra material is cheaper than a second delivery.

How do I measure a room that is not square?

Measure each wall at both ends and use the longer reading. If the out-of-square is more than an inch or two, break the room into a rectangle plus a triangle and run both. Old houses routinely run an inch out over 15 feet.

Square Footage Calculator

Pick the shape you are measuring, enter its dimensions in feet, inches, yards or metres, and this calculator returns the area in square feet, square yards, square metres and squares. Add a waste percentage and it gives you the quantity to actually order.

Shape

Measurement unit

Length / base / diameter

Rectangle: length. Triangle: base. Circle: diameter. Trapezoid: first parallel side.

Width / height

Rectangle: width. Triangle: perpendicular height. Trapezoid: second parallel side.

Second length (L-shape / trapezoid)

L-shape: length of the second rectangle. Trapezoid: distance between the parallel sides.

Second width (L-shape only)

Width of the second rectangle in the L.

Number of identical areas

Three bedrooms the same size? Enter 3.

Waste allowance(%)

10% is the working default for flooring and tile. 0% if you only want the raw area.

Material price (optional)($ / sq ft)

Leave at 0 to skip the cost line.

Area to order

264.0sq ft

240.0 sq ft measured, length × width

Square yards: 29.33sq yd
Square metres: 24.53m²
Squares (100 sq ft): 2.64squares
Measured area, no waste: 240.0sq ft

What this figure includes

This is a plane-area calculation from the dimensions you type. It measures floor or wall area only — it does not follow a slope, allow for out-of-square rooms, deduct closets, islands or fireplaces, or account for a pattern that forces longer cuts. The optional cost line is material only, at the price you enter, with no delivery, underlayment, adhesive or labour.

How this is calculated

An L-shape is two rectangles. Draw the split line, measure each rectangle separately, and add the two areas together.

The formula

Every shape here comes down to one of five expressions, all of them producing square feet once the dimensions are converted:

Rectangle: length × width
L-shape: (length A × width A) + (length B × width B)
Triangle: ½ × base × perpendicular height
Circle: π × radius², where radius is half the diameter
Trapezoid: ½ × (parallel side A + parallel side B) × the distance between them

Then two adjustments. Multiply by the number of identical areas, and multiply by (1 + waste ÷ 100). Unit conversion happens first: inches divide by 12, yards multiply by 3, metres multiply by 3.28084. Convert before you multiply, never after, or you will square the conversion error.

The L-shape, which is where people get stuck

Most rooms are not rectangles, and the L is the most common exception — a kitchen that wraps around a pantry, a living area with a bump-out, a patio with a corner taken off. There is no L-shape formula worth memorising. Draw the room, then draw one straight line that cuts it into two rectangles. Measure each rectangle on its own and add the two areas.

The trap is double-counting the overlap. Once you have drawn the split line, the second rectangle starts where the first one ends. If the total width of the building is 30 ft and rectangle A is 20 ft wide, rectangle B is 10 ft wide — not 30. Measure the two pieces as they exist on the floor after the split, not as whole-building dimensions.

Any shape with more corners works the same way. A U-shape is three rectangles. A room with an angled corner is a rectangle plus a triangle. Break it down, run each piece, add the results.

A worked example

A kitchen and dining area in an L. The main run is 20 ft by 12 ft. The dining bump-out, measured after the split line, is 10 ft by 6 ft. You are laying vinyl plank and allowing 10% for cuts.

Rectangle A: 20 × 12 = 240 sq ft
Rectangle B: 10 × 6 = 60 sq ft
Measured area: 240 + 60 = 300 sq ft
With 10% waste: 300 × 1.10 = 330 sq ft
In square yards: 330 ÷ 9 = 36.7 sq yd
In square metres: 330 ÷ 10.764 = 30.7 m²
In squares: 3.3

Order 330 sq ft. If the plank comes in 24.5 sq ft cartons, that is 13.5 cartons, so you buy 14.

Why the same measurement gets ordered four different ways

This is the real reason people end up here. One 300 sq ft floor is:

Flooring: sold by the carton, each carton printed with its square-foot coverage. Divide and round up.
Carpet: still quoted per square yard in much of the trade. Divide square feet by 9. It also comes on a 12 ft roll, so a 13 ft room wastes a full foot of width across its whole length — carpet waste is about the roll, not the room.
Paint: by coverage, roughly 350–400 sq ft per gallon per coat, and you are measuring walls rather than floor.
Sod: by the pallet, typically 400–500 sq ft, or by the pallet-and-piece.
Tile: by the box, and diagonal or herringbone layouts push waste from 10% to 15–20%.

Nothing about the measurement changes. Only the unit does. Get the square feet right once, then convert.

Measuring properly

Measure at floor level, not at counter height. Rooms are rarely square, so take each dimension at both ends and use the larger one. Measure into doorway openings and closets if the finish carries through them, and subtract permanent islands and hearths only if they are genuinely staying. When a number falls between two carton counts, buy the extra one — the attic box that matches your dye lot is worth more in five years than the refund is today.

Cost figures last reviewed 9 Sept 2026 · Placeholder mid-range finish-material price per square foot, used only for the optional cost line on the square footage tool.

Frequently asked questions

How do I calculate the square footage of an L-shaped room?: Split it into two rectangles with one straight line, measure each rectangle separately, and add the two areas. Measure the second rectangle as it exists after the split, not as a whole-building dimension, or you will double-count the overlap.
How many square feet are in a square yard?: Nine. A square yard is three feet by three feet. To convert square feet to square yards, divide by 9 — a 300 sq ft room is 33.3 sq yd. Carpet is still commonly quoted this way.
What is a 'square' in construction?: One square is 100 square feet. Roofing and siding are both ordered in squares, so a 2,400 sq ft roof is 24 squares. It is not a square that is one unit on a side, and mixing it up by a factor of 100 is a costly mistake.
How much waste should I add?: Ten percent for straight-lay flooring and tile in a simple rectangular room. Fifteen percent for diagonal or herringbone patterns, small cut-up rooms, or large-format tile. Zero if you only want the true measured area.
Do I include closets and doorways?: Include them if the finished surface continues into them, which for flooring it usually does. Exclude built-in cabinetry, kitchen islands and hearths that are staying put. When in doubt include it — the extra material is cheaper than a second delivery.
How do I measure a room that is not square?: Measure each wall at both ends and use the longer reading. If the out-of-square is more than an inch or two, break the room into a rectangle plus a triangle and run both. Old houses routinely run an inch out over 15 feet.