OSB Calculator
Calculate how many 4x8 OSB sheets you need for subfloor or sheathing from your area, with 10% waste and total cost.
How this calculator works
A standard 4 ft x 8 ft OSB sheet covers 32 square feet, the same coverage as plywood. This calculator divides your total area by that coverage figure and rounds up to a whole sheet.
Formula: Sheets = Area (sq ft) ÷ 32 sq ft per sheet, rounded up.
Worked example
A 24 ft x 20 ft area (480 sq ft):
- Area: 24 x 20 = 480 sq ft
- Sheets: 480 ÷ 32 = 15 sheets
- At $30/sheet, that’s 15 × 30 = $450.00 before waste.
Coverage reference
| Area | Sheets needed (32 sq ft/sheet) |
|---|---|
| 120 sq ft | 4 sheets |
| 480 sq ft | 15 sheets |
| 1,920 sq ft | 60 sheets |
How to measure your area
Measure the length and width of the floor, wall, or roof section being sheathed. If you’re comparing OSB against plywood for the same job, this calculator’s sheet count will match either material since both come in the same 4 ft x 8 ft size — only the price per sheet changes your total.
Frequently asked questions
What size is a standard OSB sheet?
This calculator assumes a standard 4 ft x 8 ft OSB (oriented strand board) sheet, covering 32 square feet — the same footprint as standard plywood, which makes the two materials directly interchangeable in sheet-count terms.
Why is OSB usually cheaper than plywood?
OSB is manufactured from wood strands compressed and glued in layers rather than full veneer sheets, which is generally a cheaper manufacturing process than plywood's peeled veneers. Pricing gaps between the two shift with lumber markets, so it's worth checking current pricing on both before committing.
Does OSB handle moisture as well as plywood?
Generally no — OSB tends to absorb water at cut edges and swell more than plywood when exposed to moisture, and it can be slower to dry out afterward. For roof sheathing or subfloor in areas prone to leaks or high humidity, some builders prefer plywood or make sure OSB edges are sealed.
How much waste should I add for OSB?
10% is standard for a straightforward rectangular subfloor or wall layout. Complex floor plans with lots of jogs and cutouts for stairwells or chases should use 15% to avoid a mid-job material run.
Is OSB rated the same as plywood for structural sheathing?
Both are engineered wood panels with span ratings printed on the sheet (like 32/16), and building codes generally treat them as structurally equivalent when the span rating matches your framing spacing. Always confirm the panel's span rating meets your local code for the specific application — floor, wall, or roof.
Estimates only. Verify quantities with your supplier before purchasing.