Choose the surface being covered
Record which surface consumes the material: room floor, individual wall, deck/patio surface or measured lot footprint. A floor area is not wall coverage; a lot footprint is not a boundary survey. Record the datum and units next to the sketch. The Construction Square Footage Calculator keeps area units together rather than converting an unexplained single number.
Decompose without overlap
For a rectangle measure perpendicular length and width. For a triangle measure a base and its perpendicular height, not a sloping side. For a circle measure diameter across the centre, then enter half as radius. A trapezoid needs its two parallel sides and their perpendicular separation.
For an L shape, draw a line dividing it into two rectangles and label the line. Each piece must cover unique space. For mixed sections, use the multiple-area mode and choose each row's shape. This dimension-only worksheet cannot detect overlap or containment. Use located coordinate geometry when those checks are needed.
Worked L-shaped surface
For the loadable L-shaped record, draw Main at 12 × 10 ft and the adjacent Wing at 6 × 4 ft outside it. Label their shared boundary so the two rectangles cannot overlap. Locate the 2 × 3 ft planter wholly inside one included section, and mark it as an exclusion only if the selected material will not cover it. Transfer Main, Wing and planter as three separately named rows. Keep their locations on the sketch because the worksheet stores dimensions rather than coordinates; the area methodology explains the subtraction.
Check exclusions before purchasing
Subtract only an opening that actually excludes the selected material. Do not subtract a doorway from floor coverage merely because it is an opening in a wall. Do not count two overlapping exclusions twice. Gross versus net area is a material decision, separate from waste and whole-stock rounding.
Move to Pavers or Deck Boards for physical layouts and product purchases. For drywall, see opening subtraction and sheet placement. For a selected layer depth, continue to Cubic Yard.
Normal construction uses the international foot. NIST's revised foot conversions identify the obsolete survey foot and modern area relationships. See the area formulas for exact conversions and rounding.