Method
Gross area = length × width. Net area subtracts the rectangular cut-out. Order area = net area × (1 + waste percentage/100).
Worked example
A 12 ft by 10 ft room is 120 ft². Subtract a 2 ft by 3 ft cut-out to get 114 ft². Adding 10% waste gives 125.4 ft² of material before rounding to whole packs.
Assumptions and limits
Shapes are ideal plan figures. For irregular rooms, split the plan into nonoverlapping shapes and add up to four of them. Rectangle cut-outs must fit within the room, and an inner diameter must be smaller than the outer one. Waste varies by material, pattern and installation method.
Shapes and formulas
Each shape is calculated in the entered unit and shown with your numbers substituted. Areas are summed before the waste allowance is applied, and the optional price multiplies the order area including waste.
- Rectangle: length × width − cut-out length × cut-out width.
- Circle: π/4 × diameter².
- Triangle: ½ × base × perpendicular height.
- Trapezoid: (side a + side b) ÷ 2 × height.
- Circular border (annulus): π/4 × (outer diameter² − inner diameter²).
- Rectangular border: (length + 2 × border)(width + 2 × border) − length × width.
Worked example: several areas
A 12 ft by 10 ft room (120 ft²) opens into a trapezoid-shaped nook with parallel sides of 12 ft and 8 ft, 6 ft apart (60 ft²). Together they are 180 ft²; with 10% waste the order is 198 ft², and at 4.50 per ft² the material costs 891.