Plywood Calculator
A 40 ft run of wall at 8 ft, minus one 3 by 7 opening, plus 10 percent waste, is 328.90 ft². That is 11 sheets of a 4 by 8 face.
Last updated . Walls is the opening mode. Length starts at 40 ft and height at 8 ft. Waste starts at 10. No price.
A plywood calculator for walls, a floor, or roof sheathing. An OSB calculator is the same face: the panel name does not change the sheet count. On a roof, the footprint grows by the overhang on every side, then √(1 + (pitch ÷ 12)²) stretches that plan. That root stays exact until the square feet are rounded.
Squares of shingles, not sheets: roofing calculator. Studs under the wall sheets: stud calculator. Interior boards: drywall calculator.
Plywood and OSB sheets
A 4×8 face is 32 square feet and a 4×10 face is 40. OSB uses the same face. Waste opens at 10. On a roof, overhang is added on every side, then the unrounded slope factor stretches the plan. That factor is not shortened first.
Results
How the sheet count is built
Walls multiply the summed lengths by one height. A floor multiplies length by width. A roof first adds the overhang twice to the length and twice to the width, then multiplies by the unrounded slope factor √(1 + (pitch ÷ 12)²). Openings are a width, a height, and a count, taken off after that stretch, because a roof opening is measured on the sloped surface. Order is the net times (1 + waste ÷ 100). Sheets are that order divided by the face, rounded up.
The 4×8 choice is a 32.00 ft² face. The 4×10 choice is 40.00 ft². Custom is whatever width and length you type, in the units beside those boxes. OSB and plywood share that face. Waste opens at 10 so a cut allowance is already in the first answer. Set it to 0 when you want the bare net. This page does not price a sheet and does not invent a span rating.
Sheet counts for the opening cases
| Case | Net | With waste | Face | Sheets |
|---|---|---|---|---|
| Wall 40 × 8, one 3 × 7, 10 percent, 4×8 | 299.00 ft² | 328.90 ft² | 32.00 ft² | 11 |
| Same wall, 4×10 | 299.00 ft² | 328.90 ft² | 40.00 ft² | 9 |
| Floor 16 × 12, no opening, 10 percent, 4×8 | 192.00 ft² | 211.20 ft² | 32.00 ft² | 7 |
| Roof 24 × 12, 6/12, no overhang, waste 0 | 321.99 ft² | 321.99 ft² | 32.00 ft² | 11 |
| That roof with 10 percent waste | 321.99 ft² | 354.19 ft² | 32.00 ft² | 12 |
| Roof 24 × 12, 1 ft overhang, 6/12, 10 percent | 406.96 ft² | 447.66 ft² | 32.00 ft² | 14 |
Worked example
Leave Walls, 40 ft, 8 ft, one opening 3 ft by 7 ft, waste 10, and 4×8. Net area reads 299.00 ft² · 27.78 m². With waste reads 328.90 ft² · 30.56 m². Sheets reads 11. The opening is 21 ft², so the bare wall of 320 drops to 299, and 299 × 1.10 = 328.90. 328.90 ÷ 32 = 10.28, which rounds up to 11.
Plywood and sheathing questions
How many sheets does the opening wall need?
Leave Surface on Walls, length 40 ft, height 8 ft, one opening 3 ft by 7 ft, waste 10, and sheet face 4×8. Net area reads 299.00 ft² · 27.78 m². With waste reads 328.90 ft² · 30.56 m². Sheet face reads 32.00 ft². Sheets reads 11.
How many sheets for a 16 by 12 floor?
Set Surface to Floor, length to 16 ft, and leave width at 12 ft. Set the opening count to 0 and leave waste at 10. Net area reads 192.00 ft² · 17.84 m². With waste reads 211.20 ft² · 19.62 m². Sheets reads 7.
What changes if the face is 4 by 10?
Put the wall back to 40 ft by 8 ft, one 3 by 7 opening, and waste 10. Change Sheet face to 4×10. Net area stays 299.00 ft² · 27.78 m² and With waste stays 328.90 ft² · 30.56 m². Sheet face reads 40.00 ft². Sheets reads 9, because 328.90 ÷ 40 rounds up.
How many roof sheets on a 24 by 12 footprint at 6/12?
Set Surface to Roof, length 24 ft, width 12 ft, overhang 0, pitch 6, opening count 0, and waste 0. Net area reads 321.99 ft² · 29.91 m². With waste matches it. Sheets reads 11. The stretch is the full square root of 1.25, about 1.118034, times 288. Multiplying 288 by a rounded 1.118 would print 321.98, and this page does not do that.
What does 10 percent waste, or a 1 ft overhang, do to that roof?
On the same 24 by 12 roof at pitch 6, set waste to 10 and leave overhang at 0. With waste reads 354.19 ft² · 32.91 m² and Sheets reads 12. Then set overhang to 1 ft on each side and leave waste at 10 and the opening count at 0. Net area reads 406.96 ft² · 37.81 m². With waste reads 447.66 ft² · 41.59 m². Sheets reads 14. The plan is 26 by 14 before the slope stretch. Openings, if you add any, come off after that stretch.
Does the panel name change the count?
No. Plywood and OSB use the face you pick. A 4×8 face is 32.00 ft² and a 4×10 face is 40.00 ft². Custom multiplies the width and length you type. Waste starts at 10 as a planning allowance, not a code percent.
What if a measurement is missing or the opening swallows the surface?
Clear the wall length and the results go to dashes. The note reads: Enter a wall length and a wall height, each greater than zero. On Floor the note reads: Enter a floor length and a floor width, each greater than zero. On Roof a blank footprint reads: Enter a footprint length and width, each greater than zero. A negative overhang on the roof reads: Overhang cannot be negative. A blank pitch reads: Enter a pitch greater than zero. A blank waste reads: Enter a sheet waste percent of zero or more. An opening at least as large as the surface reads: The opening is at least as large as the surface, so no sheet remains.