A house with 140 feet of 8 ft exterior walls, six 3 × 4 ft windows and two doors needs 35 sheets of 4 × 8 OSB: 1,120 ft² of wall less 112 ft² of openings is 1,008 ft², plus 10 % waste is 34.7 sheets. They take about 2,200 6d nails. The calculator above counts OSB or plywood for walls, a roof, a subfloor or any area you enter, and draws how the panels lay out.
How the calculator works
Choose what you are sheathing. For walls, enter their total length and height and list the windows and doors; for a roof, the building size, pitch and overhangs; for a subfloor, the length and width; or enter any area directly. Then pick the panel — OSB or plywood, 4 × 8, 4 × 9 or 4 × 10 ft, the thickness and the framing spacing — and the waste.
Walls
Wall sheathing is the wall length times the height, less the openings. 4 × 8 panels stood vertically cover an 8 ft wall in one piece; 9 and 10 ft panels reach from the sill to the top plate on taller walls and cover the rim joist too. Deduct the openings, but keep 10–15 % waste: the cuts around windows are mostly offcuts.
Roofs
A roof is its plan with the overhangs times the slope factor √(1 + (pitch/12)²) — for a 40 × 28 ft gable with 12 in overhangs at 6/12, 1,409 ft², or 49 sheets with 10 %. Lay the panels with the long side across the rafters and stagger the end joints.
Subfloors
A subfloor is length × width: a 40 × 28 ft floor is 1,120 ft², 37 sheets of 23/32 in tongue-and-groove with 5 % waste. Long side across the joists, end joints staggered by at least two joists.
Nails
| Panel | Nail (IRC Table R602.3(1)) | Spacing |
|---|---|---|
| Up to ½ in, walls and floors | 6d common, 2 × 0.113 in | 6 in on edges, 12 in on intermediate supports |
| Roofs, and panels over ½ in | 8d common, 2½ × 0.131 in |
A 4 × 8 sheet on studs at 16 in takes about 62 nails: 48 along its edges and 14 on the two studs in between.
Common mistakes
- Roof area from the floor plan. Add the overhangs and the slope.
- No gaps. Leave ⅛ in between panels so they can swell without buckling.
- Thickness that doesn't match the spacing. Check the span rating stamped on the panel against the framing.
For the framing behind the sheathing, use the Board Foot Calculator and the Rafter Span Calculator.