Square Footage Calculator
Turn room dimensions into square feet, square yards, square metres and roofing squares, with a deduction for openings.
Square footage is the number every other material estimate is built on, and it is also the number most often got wrong. Flooring is sold by the carton, roofing by the square, landscaping fabric by the roll, and all three are quoted in units you have to convert from square feet before you can order anything.
The trap is not the multiplication. It is the shape of the room. A closet, a bay window, a chimney breast or a doorway recess all change the area, and measuring a single length and width across the widest points overstates what you need to cover. Break an irregular room into rectangles first, then add them up.
How this calculator works
Every field is editable and the result updates as you type — nothing is submitted anywhere, all the maths runs in your browser. That matters for a number you are about to spend money on: you can see exactly which input moved the answer, and by how much.
What this calculation assumes
Assumes rectangular areas measured at their true dimensions, not across an L-shaped room in a single pair of numbers. Sloped ceilings, bay windows and openings with returns all need to be split out and measured separately.
Treat the result as an order-of-magnitude check rather than a final quantity. Product packaging changes, regional labour rates vary by a factor of two, and no calculator has seen your actual site.
Frequently asked questions
Do I include closets in the square footage?
For flooring and paint, yes — you are covering that floor and those walls. For an estate-agent listing, floor area usually excludes closets and is measured to the inside face of the walls. Decide which number you need before you start, because mixing the two is the most common source of a short order.
How do I measure an L-shaped room?
Split it into two rectangles along the inner corner, measure each one, and add the results. Do not measure the longest wall and the longest depth and multiply — that treats the missing corner as solid floor and can overstate a room by 20% or more.
What is a roofing square?
One hundred square feet of roof surface. Shingles are sold by the square, so a 2,400 sq ft roof is 24 squares, plus waste. Note this is roof surface area, not the footprint of the house — a pitched roof always measures larger than the floor below it.
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