Checked 15 October 2026. What was checked. How these pages are maintained.
Area formula
A rectangle is length × width. Add every room. 12 ft × 10 ft is 120 sq ft. In metres, 3.6 m × 3 m is 10.8 m². Closets and hallways count if you are buying flooring for them.
Odd rooms: split into rectangles and add them as extra rows. For paint or flooring, many stores tell you to add 10% waste. This page reports raw area only.
Worked example
A room 12 ft by 14 ft is 168 sq ft. Two of those plus a 10×10 is 436 sq ft. In metres, 4.0 m × 3.5 m is 14 m².
Closets and bump-outs are extra rectangles. For paint or flooring, add waste (often 10%) rather than assuming the floor plan is the order quantity.
Rectangles, then the pieces that are not
Each row is length times width. A living room 18 ft by 13 ft is 234 sq ft. A bedroom 9 ft by 8 ft is 72 sq ft. Together they are 306 sq ft. An L-shaped room is two rectangles: measure the two blocks and add a row for each. A triangular bay is base × height ÷ 2. The form has no triangle switch. Put that area in as a row with width 1 and length equal to the area, and label it so you remember why.
The unit control applies to every row. Feet and metres in the same total are not converted. A 4 m by 3 m room is 12 m² only if the control says metres. Leaving it on feet makes that row 12 sq ft, which is a small closet, not a room. One square metre is about 10.764 square feet if you need to compare a metric plan with a foot total. Do that conversion outside the sum, or remeasure.
The order quantity is larger than the floor
The page also shows the total plus 10 percent, which is a common waste allowance for boards that are cut and for tile that breaks. 306 sq ft plus 10 percent is 336.6. Carpet seams, a pattern that has to match, and boards that are stained from one dye lot can need more than 10 percent. The raw total is the floor. The 10 percent line is a starting order, not a quote. Paint is a wall problem, not a floor problem. The paint calculator uses wall height and subtracts doors and windows, which this page never asks for.
Common questions
How do I do a triangle?
Area = base × height ÷ 2. Enter that area as length = the area and width = 1, or split the room.
Square metres to square feet?
1 m² ≈ 10.764 sq ft. This page totals in the unit you picked; it does not mix units in one run.