Square Footage Calculator

Break it into rectangles. Almost every "irregular" room is two or three squared-off boxes plus a bump-out. Stand in the room and draw it on paper, then slice it along the corners until every piece has four right angles. Measure each box separately, calculate each one, and add them together.

Use L-Shape mode for a two-box room, or Multiple Rooms mode and add each box as its own entry (call them "Main box" and "Bump-out") for anything more complicated. Bay windows, alcoves and angled corners can be measured as triangles or trapezoids and added the same way.

It depends on why you are measuring. For materials, include any closet you are actually going to floor, paint or tile. Flooring usually runs into a reach-in closet, so measure it and add it; a walk-in closet is effectively another small room.

For listing or appraisal square footage, the common standard counts finished, heated space measured to the outside of the exterior walls, which includes closets inside that footprint but excludes garages, unfinished basements and open two-story voids. Materials math and listing math give different numbers on purpose, so never reuse a listing figure to buy flooring.

Because you never install a floor in whole pieces. Every plank cut at a wall, every tile trimmed around a doorway and every carpet seam creates an offcut you cannot use. Buying the exact square footage guarantees a second trip, and a second trip often means a different dye lot or batch that will not match.

Ten percent is the usual minimum for a straight-lay pattern in a simple rectangular room. Go to 15% for diagonal or herringbone layouts and for rooms with lots of jogs, and 20% for large-format tile, patterned carpet or long narrow spaces. Keep the leftovers: they are your repair stock.

Carpet is still quoted and sold by the square yard in many stores, and the conversion is simple: 1 square yard = 9 square feet. Divide your square footage by 9. A 12 ft x 15 ft bedroom is 180 sq ft, which is 20 sq yd.

One catch: broadloom carpet comes off a roll in a fixed width, usually 12 ft. If your room is 13 ft wide you pay for a 12 ft roll plus a seamed strip, and the waste is far more than 10%. Ask the store to do a roll-width layout before you buy, and use this calculator's square yard figure as the sanity check on their quote.

Flooring is the floor area: length times width of the room, plus closets, minus permanent fixtures like a kitchen island base or a tub footprint. That is exactly what this calculator gives you.

Paint is wall area, which is a different measurement: add up the length of every wall to get the perimeter, multiply by the ceiling height, then subtract roughly 20 sq ft per door and 15 sq ft per window. A 12 ft x 15 ft room is 180 sq ft of floor but about 216 sq ft of wall at an 8 ft ceiling. Run the numbers on the paint calculator instead of reusing your floor figure.