Square Footage Calculator

Square footage is the area in feet, so every measurement has to be in feet before you multiply. Inches convert by dividing by 12: 14 ft 6 in is 14 + 6 ÷ 12 = 14.5 ft. Multiplying feet by inches without converting is the single most common square footage error and inflates the answer roughly twelve-fold.

From there the shape decides the formula. A rectangle is length × width, a triangle is base × height ÷ 2, and a circle is π × radius², where the radius is half the diameter. Square yards divide by 9 and square metres multiply by 0.09290304. The overage percentage is applied last, to the purchase figure only, so you can still see the true measured area.

• Decimal feet = feet + (inches ÷ 12)
• Rectangle area (sq ft) = length × width
• Triangle area (sq ft) = base × height ÷ 2
• Circle area (sq ft) = π × (diameter ÷ 2)²
• Total area = shape area × number of identical areas
• Purchase area = total area × (1 + overage % ÷ 100)
• Square yards = sq ft ÷ 9 · Square metres = sq ft × 0.09290304
• Boxes = round up(purchase area ÷ coverage per box)

The measured area is the true size of the space; the waste-adjusted figure is what to buy. Box counts round up because part-cartons are not sold, so the coverage you end up with is usually a little over.

Common mistakes and assumptions

• Multiplying feet by inches instead of converting inches to decimal feet first.
• Using a sloping side as the height of a triangle rather than the perpendicular height.
• Entering the radius where the calculator asks for a circle's diameter, which quarters the area.

Someone is buying vinyl plank for a bedroom measuring 14 ft 6 in by 12 ft 3 in, allowing 10% for cuts, with boxes that cover 22.5 sq ft at $48 each.

1. 1Convert to decimal feet: 14 ft 6 in = 14.5 ft, and 12 ft 3 in = 12.25 ft.
2. 2Area = 14.5 × 12.25 = 177.63 sq ft (19.74 sq yd, 16.50 sq m).
3. 3Add 10% for cuts: 177.63 × 1.10 = 195.39 sq ft to buy.
4. 4Boxes = 195.39 ÷ 22.5 = 8.68, rounded up to 9 boxes.
5. 5Nine boxes cover 202.5 sq ft and cost 9 × $48 = $432 before tax.

How do I calculate the square footage of a room?

Measure the length and width in feet, convert any leftover inches to decimals by dividing by 12, then multiply. A room 12 ft 6 in by 10 ft is 12.5 × 10 = 125 square feet. For an L-shaped room, split it into rectangles, work each one out, and add them.

How many square feet are in a square yard?

Nine. A square yard is 3 ft × 3 ft, so divide square feet by 9 for square yards and multiply by 9 to go the other way. Carpet is often quoted per square yard while the room is measured in feet, which is where the confusion starts.

How much extra flooring should I buy?

Ten percent over the measured area is the usual allowance for straight-lay planks or tiles in a simple room. Go to 15% or more for diagonal and herringbone layouts, patterned material that has to align, or rooms with lots of angles and closets, since every cut leaves an offcut you cannot use.

Do I include closets, alcoves, or cabinets?

Include anything that gets floor covering, including closets and alcoves, and exclude the footprint of fixed cabinets, islands, and hearths if the material stops at them. When in doubt, include the area — leftover flooring is cheaper than a second order in a different batch.

How do I find the square footage of a circle?

Use π × radius², with the radius as half the diameter in feet. A round patio 12 ft across is π × 6² = 113.1 square feet. Select the circle option above and enter the diameter — the calculator halves it for you, which avoids the most common mistake here.

Does square footage tell me how much paint I need?

Only if you measure the walls rather than the floor. Paint coverage is based on wall area — perimeter × ceiling height, minus doors and windows — and one gallon typically covers 350-400 square feet per coat. Use this calculator per wall, then add the results.

Why does my measured square footage differ from the listing?

Property listings usually quote gross living area measured to the exterior walls and follow local measurement standards, while you are measuring the inside floor. Interior finished area is normally smaller, and for buying material the interior figure is the one that matters.