Floor Area Calculator

Nobody can run a tape across a whole house, because walls get in the way. Floor area is therefore a sum: measure each room on its own, multiply its length by its width, and add the answers. All the rooms here share one unit, so pick the one your tape reads in before you start.

Formula

Total = (l₁ × w₁) + (l₂ × w₂) + … − deduction

l, w

the length and width of each room, in the same unit

deduction

any area you have chosen to leave out, such as a stairwell

How to work out total floor area

Take one room per row and go through the house in a fixed order, so that nothing gets missed or counted twice. Hallways, landings and utility rooms count as rooms. Measure wall to wall at floor level, where baseboards and furniture are the only obstacles.

1. Choose the unit you are measuring in.
2. Enter a length and width for each room. It makes no difference which is which.
3. Leave any unused rows completely blank; they are skipped.
4. Enter a deduction if part of the floor shouldn't count.

A worked example

Take three rooms of 14 × 12 ft, 12 × 10 ft and 10 × 8 ft. Their areas are 168, 120 and 80 ft², which add up to 368 ft², or about 34.19 m². If a stairwell measuring 3 × 10 ft takes up 30 ft² of that, the floor area after the deduction is 338 ft².

The same method works in metric. Rooms of 5 × 4 m, 4 × 3.5 m and 3 × 3 m come to 20 + 14 + 9 = 43 m², which is about 462.85 ft². One square meter is about 10.76 ft², so the results list both whichever unit you measure in.

Should you deduct stairs and closets?

That depends on why you want the number, so the deduction is left optional and the calculator doesn't assume anything. If you are ordering flooring and it continues into a closet, keep the closet in. If the flooring stops at the closet door, subtract it. A stairwell opening is a hole in the upper floor, so subtract it there when you are working out how much floor that level actually has.

Enter the deduction as a single area, in the square of your chosen unit. For two or three items, add them up first: a 2 × 4 ft closet and a 3 × 10 ft stairwell make a deduction of 38 ft².

Rooms that aren't rectangles

Split an awkward room into rectangles and give each one its own row. An L-shaped living room might be a 12 × 15 ft main part plus a 6 × 8 ft alcove, which is 180 + 48 = 228 ft². If a house needs more than the six rows, run the sums one floor at a time and add the totals by hand.

For measurements in feet and inches, turn the inches into a decimal of a foot before entering them. A wall of 12 ft 6 in is 12.5 ft, and 12.5 × 10 ft is 125 ft².

Why your total may not match a listing

This calculator adds up the floor you can stand on inside each room, so it leaves out the thickness of the walls. A figure taken around the outside of the building includes them and always comes out higher. A house measuring 40 × 30 ft on the outside has a footprint of 1,200 ft², and its rooms will add up to less than that. Before comparing two numbers, find out which way each was measured and whether garages, basements or balconies were included, because practice varies between countries and between agents.

In India, homes are often quoted by carpet area and built-up area, which have their own definitions. The carpet area calculator converts between those.

Frequently asked questions