Plywood Calculator
This plywood calculator estimates how many sheets of plywood or OSB to buy to sheathe a wall, a floor or deck, or a roof. Add each section as length × width (or wall height), take off the openings, add gable triangles for a wall or the roof pitch for roof sheathing, and choose a 4 × 8, 4 × 9 or 4 × 10 ft sheet. It adds a waste allowance, rounds up to whole sheets and can show a weight range for the sheets.
Quick answer: sheets = area × (1 + waste) ÷ sheet area, rounded up. A 30 × 9 ft wall is 270 sq ft. Take off 36 sq ft of openings for 234 sq ft, and with 10% waste that is 257.4 sq ft. Divided by 32 sq ft per 4 × 8 sheet that is 8.04, so buy 9 sheets.
Sheets of plywood or OSB depend on the area you cover, the waste for cuts and the size of one sheet. Add up length × width for each section (or wall length × height), take off openings, add any gable triangles for a wall, or multiply a roof's plan area by its pitch factor. Then add the waste, divide by the area of one sheet (32 sq ft for a 4 × 8) and round up to whole sheets.
Example: a 30 × 9 ft wall is 270 sq ft. Take off 36 sq ft of openings for 234 sq ft, and with 10% waste that is 257.4 sq ft. Divided by 32 sq ft that is 8.04, so buy 9 sheets of 4 × 8 ft. With no waste it would be 7.31, which rounds up to 8.
Method
How this calculator works
The area math is exact. The two choices that move the count are the sheet size you buy and the waste you plan for, and everything structural, like thickness and nailing, is left to the grade stamp, the maker and the code.
Area to cover
A wall is the sum of length × height for each section, plus any gable triangles, minus the openings you will not cover. A floor or deck is length × width. A roof is the plan area times the pitch multiplier, and the plan size includes the eave and rake overhangs, not the sloped length. The sections are added first, so waste and rounding apply once to the total.
Wall area = Σ (Length × Height) + Gables × (½ × Gable width × Gable rise) − OpeningsFloor or deck area = Σ (Length × Width)Roof area = Plan area × √(1 + (Pitch ÷ 12)²)Sheet size
A 4 × 8 ft panel is the standard size, which is 32 sq ft. APA says standard OSB panels are 4 × 8 feet, and Weyerhaeuser lists its southern yellow pine plywood as 4 × 8 ft. Georgia-Pacific also lists panels sized for 4 × 9 and 4 × 10 ft. Panels are made a hair under nominal (a 4 × 8 square-edge OSB panel is 3 ft 11 7/8 in by 7 ft 11 7/8 in, or 31.875 sq ft), and the calculator counts the nominal area, a 0.4% difference it does not model.
Sheet area = 32 (4 × 8), 36 (4 × 9) or 40 (4 × 10) sq ft, or Width × Length for a custom sizeWaste and rounding
No standards body sets a sheathing waste. The calculator starts at 10%, the figure one commercial plywood calculator uses for subfloor and roof sheathing, with 15% for many cuts or openings. It is a starting point you change from 0 to 40%. It also shows the sheets you would need with no waste, so you can see what the allowance adds.
Sheets = round up (Area × (1 + Waste ÷ 100) ÷ Sheet area)Weight range
If you pick a thickness, the calculator multiplies the sheets by the sheet area and a pounds-per-square-foot range from the Boise Cascade Technical Note GE-1, which cites APA Technical Topic TT-019 from 1998. The note's stated validity has passed, and the table does not separate plywood from OSB. Use it for a rough lift or load, and use your supplier's figure when you need an exact weight.
Weight range = Sheets × Sheet area × (low to high lb per ft²)Sheet sizes in the calculator
| Size | Area | What the sources say |
|---|---|---|
| 4 × 8 ft | 32 sq ft | The standard panel. APA: standard OSB panels are 4 × 8 feet. Weyerhaeuser: all of its southern yellow pine plywood panels are 4 × 8 ft. |
| 4 × 9 ft | 36 sq ft | Georgia-Pacific lists OSB sheathing sized for 4 × 9 ft. |
| 4 × 10 ft | 40 sq ft | Georgia-Pacific lists OSB sheathing sized for 4 × 10 ft. |
| Custom size | Width × length | For any other panel. APA says oversized panels exist up to 8 × 24 ft for panelized systems. |
Weight of a sheet, from a dated industry table
| Panel thickness | Pounds per sq ft | One 4 × 8 sheet | One 4 × 10 sheet |
|---|---|---|---|
| 11/32 or 3/8 in | 1.0 to 1.2 | 32.0 to 38.4 lb | 40.0 to 48.0 lb |
| 15/32 or 1/2 in | 1.4 to 1.7 | 44.8 to 54.4 lb | 56.0 to 68.0 lb |
| 19/32 or 5/8 in | 1.8 to 2.1 | 57.6 to 67.2 lb | 72.0 to 84.0 lb |
| 23/32 or 3/4 in | 2.2 to 2.5 | 70.4 to 80.0 lb | 88.0 to 100.0 lb |
| 7/8 in | 2.6 to 2.9 | 83.2 to 92.8 lb | 104.0 to 116.0 lb |
| 1 1/8 in | 3.3 to 3.6 | 105.6 to 115.2 lb | 132.0 to 144.0 lb |
What each field does
| Field | What to enter |
|---|---|
| What are you covering? | Wall (length × height), Floor or deck (length × width) or Roof (plan size and pitch). |
| Sections: Length, and Width or wall height | One row per section, up to 30 (use Add section). For a roof, the plan size with overhangs, not the slope. |
| Sheet size | 4 × 8 ft (32 ft²), 4 × 9 ft (36 ft²), 4 × 10 ft (40 ft²) or Custom size. 4 × 8 is the standard panel. |
| Custom sheet width and length | Used with Custom size. |
| Roof pitch (rise per 12 in run) | For a roof. Starts at 6, meaning 6/12. |
| Openings, total area | For a wall. Doors and windows you will not cover. |
| Gable ends, Gable width and Gable rise | For a wall. Each gable is a triangle of ½ × width × rise. |
| Waste allowance | Starts at 10%. Typical allowance, adjust for your job: about 10%, 15% with many cuts or openings. 0 to 40%. |
| Thickness (for the weight) | Optional. Pick a panel thickness to show the weight range, or Do not show the weight. It does not change the sheet count. |
Worked example: a 30 × 9 ft wall
Arithmetic checkedThese are the calculator's own example values: one wall section, 36 sq ft of openings, no gables, 4 × 8 ft sheets and 10% waste.
| Step | Math | Result |
|---|---|---|
| Wall area | 30 × 9 | 270 sq ft |
| Net wall area | 270 + 0 − 36 | 234 sq ft |
| Area with waste | 234 × (1 + 10 ÷ 100) | 257.4 sq ft |
| Sheets, before rounding | 257.4 ÷ 32 | 8.044 |
| Sheets to buy | rounded up | 9 sheets |
| Sheets with no waste | 234 ÷ 32 = 7.31, rounded up | 8 sheets |
| You would see | 9 sheets to buy, with waste | |
Disclaimer
Results are planning estimates based on the dimensions and assumptions you enter. They are not engineering, structural or building-code advice. Product yields, densities and coverage vary by manufacturer, batch and site conditions. Check product labels, your supplier and your local building department before you order materials or start work. Read the full calculation disclaimer.
Accuracy
What affects your estimate
The formula is simple. What changes the answer is the sheet size, the waste, the roof pitch and how the framing and openings lay out.
Sheet size changes the count
The same 257.4 sq ft takes 9 sheets of 4 × 8 ft, 8 sheets of 4 × 9 ft (257.4 ÷ 36 = 7.15) and 7 sheets of 4 × 10 ft (257.4 ÷ 40 = 6.44). Check what your supplier stocks and whether you can carry and lift the longer sheets.
Waste can add a whole sheet
With no waste the example is 234 ÷ 32 = 7.31, so 8 sheets. With 10% it is 8.04, which is just over 8, so the ninth sheet is needed. A result that lands this close to a whole number is worth a second look at your measurements.
Roofs use the plan size and the pitch
A 24 × 40 ft plan with overhangs is 960 sq ft. At a 6/12 pitch the multiplier is 1.118, so the roof is 1,073.3 sq ft, and 10% waste makes 1,180.6 sq ft. Divided by 32 that is 36.9, so 37 sheets (34 with no waste). With 15/32 in panels the weight range is 1,658 to 2,013 lb.
Gables add triangles
Add two gables 24 ft wide and 8 ft high to the 30 × 9 ft wall. Each triangle is ½ × 24 × 8 = 96 sq ft, so the wall is 270 + 192 − 36 = 426 sq ft. With 10% waste that is 468.6 sq ft, and 468.6 ÷ 32 = 14.64, so 15 sheets.
Floors and decks
A 12 × 16 ft floor is 192 sq ft. With 10% waste that is 211.2 sq ft, and 211.2 ÷ 32 = 6.6, so 7 sheets. With no waste it would be exactly 6 sheets, which leaves no room for a miscut.
Thickness is nominal, and it does not change the count
The thickness list only sets the weight. APA calls the Performance Category the nominal thickness used in building codes, and the real thickness is a decimal that differs: Georgia-Pacific declares 0.451 in for a 15/32 OSB panel and 0.703 in for 23/32. Read the grade stamp for the span rating and thickness you need.
This calculator estimates how many sheets to buy. Panel thickness, span rating, nailing, edge support (H-clips or tongue-and-groove), blocking and wall bracing are structural, and the calculator does not choose or check them. Use the span rating on the grade stamp, the maker's and the code's rules, and a professional for structural work. Real counts depend on the framing layout and how openings are cut. See the calculation disclaimer.
Common mistakes
Entering the slope length of a roof
The roof fields take the plan size with overhangs, and the calculator applies the pitch multiplier. Entering the sloped length and the pitch counts the slope twice.
Forgetting the gables
A wall section is a rectangle. The triangles above it are separate, and each gable adds ½ × width × rise. Leave the gable count at 0 only when there are none.
Treating the weight as exact
The range comes from one dated table that does not separate plywood from OSB, and real panels vary with species, glue and moisture. Use it for planning a lift, and your supplier's figure for loads.
Choosing thickness or nailing from a sheet count
The count says nothing about span, fastening or edge support. Follow the span rating on the grade stamp and the code for your framing spacing.
Assuming offcuts always get reused
The estimate is area divided by sheet size. Real counts depend on the framing layout and how openings are cut, so check the number of sheets against your plan and the pack label when you buy.
Questions people ask
How many sheets of plywood do I need?
Divide the area, with waste, by the area of one sheet and round up. A 234 sq ft wall with 10% waste is 257.4 sq ft, and 257.4 ÷ 32 = 8.04, so 9 sheets of 4 × 8. The guide on plywood sizes shows the sheet dimensions and weights.
What size is a standard sheet of plywood?
The standard panel is 4 × 8 ft, which is 32 sq ft. 4 × 9 and 4 × 10 ft sheets are also made, and oversized panels exist for panelized systems.
How many sheets of plywood for a roof?
Multiply the plan area, with overhangs, by the pitch multiplier, add waste and divide by 32. A 24 × 40 ft plan at 6/12 needs 37 sheets with 10% waste. If you only know the angle, the Roof Pitch Calculator gives the pitch, and the Roofing Calculator covers the shingles.
How much does a sheet of plywood weigh?
A 4 × 8 sheet of 15/32 or 1/2 in weighs about 44.8 to 54.4 lb, and a 23/32 or 3/4 in sheet about 70.4 to 80.0 lb, according to a dated Boise Cascade table that does not separate plywood from OSB. Your supplier's figure is better.
Does it work for OSB too?
Yes. The sheet count is area arithmetic, and plywood and OSB come in the same standard sizes. The weight table does not separate them.
What thickness, nailing or clips do I need?
This calculator does not say. Thickness, span rating, nailing, edge support and bracing come from the grade stamp, the panel maker, the building code and, for structural work, a professional.
How much waste should I allow?
There is no standard. A commercial plywood calculator uses 10% for subfloor and roof sheathing and 15 to 20% for custom cuts. This calculator starts at 10% and accepts 0 to 40%.
Related calculators and guides
Sources
Where the numbers come from
- APA, OSB (oriented strand board) standard panels are 4 × 8 feet, oversized panels up to 8 × 24 feet, and the Performance Category as nominal thickness, accessed October 17, 2026.
- Georgia-Pacific BlueRibbon Rated Sheathing specifications panels sized for 4 × 8, 4 × 9 and 4 × 10 ft, and declared decimal thicknesses, accessed October 17, 2026.
- Weyerhaeuser, southern yellow pine plywood all panels are 4 × 8 ft, accessed October 17, 2026.
- Boise Cascade Technical Note GE-1, Weights of Building Materials pounds per square foot of wood structural panels, a dated table past its stated validity, accessed October 17, 2026.
- Billd plywood calculator a commercial source for 10% waste on subfloor and roof sheathing and 15 to 20% for custom cuts, accessed October 17, 2026.
- NIST Handbook 44 (2026), Appendix C exact area and weight conversions for the metric view, accessed October 17, 2026.