Use this roof sheathing calculator to estimate how many OSB or plywood sheets you need for roof decking, roof sheathing replacement, or a roof repair area. It can estimate from roof plane dimensions, building footprint with a pitch factor, or a known roof square footage.
This is a material planning calculator, not a structural roof design, span rating, fastening, diaphragm, wind, snow-load, or code compliance calculator. Final roof sheathing layout still depends on rafter or truss spacing, panel rating, roof geometry, edge support, local code, and manufacturer instructions.
Estimate your roof sheathing sheets
Use only with footprint mode. Roof plane mode already includes slope.
How this estimate works
The calculator estimates roof sheathing area from measured roof planes, a building footprint with a pitch factor, a known roof square footage, or a repair area. It applies the replacement percentage, subtracts large openings, adds waste, divides by panel coverage, and adds optional extra sheets.
When this roof sheathing calculator is useful
- Estimating OSB or plywood sheets for a roof deck
- Checking a roofing material list before ordering panels
- Estimating sheathing for a gable roof, hip roof, dormer roof, garage, shed, or addition
- Planning roof sheathing replacement when soft decking or rot is suspected
- Comparing a full roof deck estimate against a partial repair estimate
What this calculator does not decide
This calculator does not choose panel thickness, span rating, exposure rating, fastening schedule, nail spacing, roof diaphragm design, wind resistance, snow-load design, or code compliance. Those depend on the roof framing, local code, manufacturer instructions, and sometimes engineering.
Do not undercount roof sheathing waste
Roof sheathing usually needs more waste allowance than a simple wall field. Hips, valleys, ridges, rakes, eaves, dormers, chimneys, vents, skylights, and hidden rot all change how many sheets are needed once the roof is opened.