Plywood & OSB Calculator
Work out how many sheets of plywood or OSB you need for walls, a subfloor or a roof. Roof pitch and overhang are included. You also get total weight, fasteners and cost, and the same area in 4×9 and 4×10 sheets.
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Sheets = area (sq ft) ÷ 32 for 4×8 panels, plus 10% for cuts, rounded up. A 40 ft run of 8 ft wall with 40 sq ft of large openings is 280 sq ft, so 10 sheets. A 40 × 30 ft house with a 6/12 roof and 12 in overhangs has 1,503 sq ft of roof, so 52 sheets.
How to use this plywood calculator
- Choose walls, floor or roof.
- Enter the dimensions. For walls, subtract garage doors and big windows; small windows are usually sheathed over and cut out. For roofs, enter the building footprint and the calculator adds the pitch and overhang.
- Pick the panel and sheet size. The panel choice sets the weight.
- Read the order: sheets, total weight, fasteners and cost.
Sheets needed by area
| Area | 4×8 sheets (+10%) | 4×9 sheets | 4×10 sheets |
|---|---|---|---|
| 100 sq ft | 4 | 4 | 3 |
| 250 sq ft | 9 | 8 | 7 |
| 500 sq ft | 18 | 16 | 14 |
| 1,000 sq ft | 35 | 31 | 28 |
| 2,000 sq ft | 69 | 62 | 55 |
Taller sheets (4×9 and 4×10) let you sheathe a 9 or 10 ft wall in one piece, with no horizontal joint to block.
Which thickness for which job
| Use | Common panel | Notes |
|---|---|---|
| Wall sheathing | 7/16 in OSB or 15/32 in plywood | Studs at 16 or 24 in |
| Roof decking | 7/16 to 5/8 in | Thicker for 24 in spacing, tile or heavy snow. H-clips between rafters at 24 in. |
| Subfloor | 23/32 in T&G (sold as ¾ in) | Glued and screwed. Joints staggered. |
| Shed floor or walls | ½ to ¾ in | Use exterior-rated panels |
Every structural panel is stamped with a span rating such as 24/16 (roof span / floor span in inches). Make sure it matches your framing spacing.
OSB or plywood?
- OSBCheaper, consistent and the most common sheathing in new US homes. Edges swell if they stay wet, so keep it covered.
- PlywoodLighter for its strength and recovers better after getting wet. Often preferred for roofs and subfloors in wet climates.
- Install either the same wayStamp side up, long edge across the framing, ⅛ in gaps, and nails at about 6 in on the edges and 12 in in the field unless your code or a high-wind zone needs closer.
Worked example
- Roof: 40 × 30 ft house, 12 in overhangs
- 42 × 32 = 1,344 sq ft footprint
- 6/12 pitch (× 1.118)
- 1,503 sq ft of roof
- Add 10% and divide by 32
- 52 sheets of 4×8
- Weight at 7/16 in OSB
- about 2,340 lb
Frequently asked questions
How many sheets of plywood do I need?
Area ÷ 32 for 4×8 sheets, plus about 10%. A 12 × 16 ft floor needs 7 sheets.
How many square feet does a 4×8 sheet of plywood cover?
32 sq ft. A 4×9 sheet covers 36 sq ft and a 4×10 sheet covers 40.
What thickness plywood or OSB should I use?
7/16 in OSB or 15/32 in plywood for walls, 7/16–5/8 in for roofs and 23/32 in T&G for subfloors. Check the span rating against your framing.
How much does a sheet of plywood or OSB weigh?
About 45 lb for 7/16 in OSB, 48 lb for ½ in plywood, 60 lb for ⅝ in and 70–75 lb for ¾ in panels.
Do I need a gap between sheathing panels?
Yes, about ⅛ in at edges and ends, unless the manufacturer says otherwise.
What this calculator assumes
- Waste is added to the area, then sheets are rounded up. Roofs use the pitch factor for your slope and a uniform overhang.
- Weights are typical dry values and vary by brand and species.
- Fasteners are estimated at about 50 per sheet. Follow your code’s nailing schedule.