Square Footage Calculator

How do you calculate square footage?

Square footage comes from multiplying the length of a floor by its width, both measured in feet, which gives an area expressed in square feet. Take a room of 20 ft by 15 ft: multiplied together the two figures give 300 sq ft. That single rectangle covers the whole calculation for a room of that shape.

A house repeats the same operation room by room. The three rows loaded by default, 20 × 15, 14 × 12 and 12 × 11, work out at 300, 168 and 132 sq ft, which the calculator adds into 600 sq ft and splits into shares of 50%, 28% and 22%. That share column tells which room drives the order, the living room alone carrying half of it.

Wall to wall at floor level is the line to measure, since baseboards and door casings narrow a room by an inch or two higher up. A tape reads in feet and inches while the fields above take decimal feet, so the inches are divided by 12 before being typed in. A room of 12 ft 6 in goes in as 12.5 and one of 12 ft 8 in as 12.67. Appraisers working to ANSI Z765 measure to the nearest inch or the nearest tenth of a foot, then report the area to the whole square foot.

How to calculate square footage of a room that is not a rectangle

Any shape that is not a rectangle gets broken into rectangles whose areas are then added together. An L-shaped living room splits along the inside corner of the L, so a section of 14 × 10 and a second of 8 × 6 give 140 sq ft and 48 sq ft for a total of 188 sq ft, one row per part.

Closets, alcoves and the floor inside a bay window take the same treatment, one rectangle per row, named so the breakdown stays legible. A curved bay has no exact rectangular equivalent; the usual approximation boxes the curve inside the smallest rectangle that contains it, which overstates the area by a few square feet. On a flooring order that overstatement disappears into the waste allowance, though it has to come out again before the figure goes into a listing.

Square footage of common room sizes

A 10 × 12 room comes to 120 sq ft and needs 132 sq ft of flooring on the shelf at the default allowance. The rows below run those same two steps on the sizes that keep recurring in listings and flooring quotes, using 1 sq ft = 0.0929 m².

Round dimensions in a listing are worth a tape measure of their own. A room advertised as 12 × 12 that measures 11.5 by 11.8 in reality gives 135.7 sq ft, eight square feet short of the round figure and enough to move a tile order by one box.

How is square footage converted to square meters or acres?

Metric tapes and European listings work in square meters, where one square meter holds 10.7639 sq ft, so a 600 sq ft floor reads as 55.74 m² while a 40 m² apartment reads as 430.56 sq ft. Switching the Measured in field to meters keeps both readings on screen.

One acre is 43,560 sq ft, a figure inherited from the surveyor's chain of 66 ft, an acre being the strip of 66 ft by 660 ft that a team of oxen ploughed in a day. Past 4,000 sq ft the calculator adds the acre line, so a backyard of 100 × 60 shows as 6,000 sq ft and 0.138 acres, the unit a plot listing quotes.

How much extra material should be ordered above the measured square footage?

Flooring is ordered above the measured area, 10% above it on a straight-lay job, which turns 600 sq ft of measured floor into 660 sq ft of product. The order line runs that same calculation on any allowance from 0 to 50%.

• 5 to 10% for straight-lay plank or board, the share that covers the ends cut off each row and thrown away.
• 15% for a diagonal or herringbone layout.
• 20% for patterned tile that has to line up across a seam in a room with several doorways.

The leftover box then sits in a garage for years until a tile cracks and needs replacing. Dye lots, the production batches that tiles and planks come from, shift enough between runs that a fresh box rarely matches the floor already down. Tile and plank sell by the box in any case, so the counter rounds the order up to the next full box.