Measure the footprint before ordering finishes
Square footage describes a surface, rather than the perimeter around it or the volume above it. This tool handles three common plan shapes so you can measure rooms, alcoves and circular features without treating every space as a rectangle. Choose the shape first. For a rectangle enter its two adjacent sides. For a triangle enter the base and the height measured at a right angle to that base. For a circle enter the full diameter; the width field is unused. Measurements refer to the horizontal floor footprint.
Area equations and deductions
Rectangle = length × width; triangle = base × height ÷ 2; circle = π × diameter² ÷ 4The subtraction box removes a known area such as a permanent cabinet or an opening. It must use square units, not the width of a doorway. An opening larger than the selected footprint is rejected. Purchasing allowance is applied after that deduction and appears as a separate result, keeping the measured room area visible. No waste is built into the geometric equations. One square foot equals exactly 0.09290304 square metres, so conversion uses a squared length factor rather than dividing by a single metre-to-foot factor.
A room with a fitted cupboard
A rectangle measuring 5 metres by 4 metres has 20 square metres of gross footprint. A fitted cupboard occupies 2 square metres, leaving 18 square metres to cover. With a purchasing allowance of 10 percent, the quantity used for a flooring order is 19.8 square metres. The actual usable floor remains 18 square metres, equivalent to 193.75 square feet. An imperial room measuring 20 by 15 feet with 10 square feet excluded has 290 square feet of usable surface and a purchasing quantity of 319 square feet at the same allowance.
Irregular layouts and measurement habits
Divide an L-shaped room into nonoverlapping rectangles, calculate each section and add the net areas. Mark your dividing line on a sketch to avoid counting the shared corner twice. Measure a triangular bay perpendicular to its base instead of following a sloping side. Check both ends of a room if the walls taper. For flooring, measure beneath movable furniture, but decide explicitly whether permanent kitchen units will receive the new finish. A floor plan used for property listings may follow different measurement conventions from a materials order. This tool measures geometry and does not certify advertised living area.
Frequently asked questions
How do I calculate square footage?
Multiply length by width when both are in feet. A 12 by 10 foot rectangle measures 120 square feet before deductions or material allowances.
Can I enter metres?
Yes. Metric mode calculates square metres and also reports square feet. Imperial mode accepts feet and reports the equivalent square metres.
Does a circle use radius or diameter?
Enter diameter, the distance all the way across the circle through its centre. The calculator divides that value by two within the area equation.
Is waste part of the room area?
No. Net area describes the measured footprint. Area including allowance is a separate purchasing figure for cuts and offcuts.
How do I measure an L-shaped room?
Split it into two rectangles that do not overlap, record their individual results and add them. Deduct a cupboard only from the section containing it.
Last reviewed: 2026-10-03 · How we calculate