Plywood / OSB Sheathing Calculator
Estimate plywood or OSB sheets for a wall, roof, subfloor, or other flat surface. Enter the net area and the panel dimensions you plan to purchase.
How this calculator works
Enter the total flat surface area and subtract large openings such as windows or doors if you have measured them. Smaller cuts may not reduce the sheet count because the offcuts are not always reusable. Break complex surfaces into simpler shapes and add their areas before entering the total.
net area = gross area − openings panel coverage = panel width × panel length sheets = ceil(net area × (1 + allowance ÷ 100) ÷ panel coverage)
Worked example
An 800 sq ft surface with 80 sq ft of openings has 720 sq ft net area. With 4×8 ft panels and 10% extra, 720 × 1.10 ÷ 32 = 24.75, so plan on 25 sheets.
Panel coverage and layout affect the count
The default 4×8 ft panel covers 32 square feet, but products are available in other dimensions and thicknesses. The calculator rounds the sheet count up and applies your entered allowance. Actual layout, staggered joints, edge support, cutouts, and panel orientation can change the final order quantity.
Check material and installation requirements
Plywood and OSB products differ in grade, thickness, exposure rating, and approved use. This tool estimates surface coverage only; it does not specify structural panel thickness, fastening, span, or code compliance. Follow the plans, product stamp, and local building requirements.
Frequently asked questions
How many sheets of plywood do I need?
Divide the net area by the panel area, apply your waste allowance, then round up to whole sheets. A standard 4×8 ft panel covers 32 sq ft before cuts and waste.
Should I subtract windows and doors?
You can subtract measured openings from the gross area. Keep in mind that cutouts may not reduce the number of sheets if offcuts cannot be reused.
How much extra sheathing should I order?
The appropriate allowance depends on layout complexity, openings, cuts, and whether offcuts can be reused. Enter your own planning margin; the default is not a universal requirement.
Does this calculator choose plywood thickness or grade?
No. It calculates panel quantity from area and dimensions. Select material type, thickness, grade, fastening, and installation method from project plans, manufacturer guidance, and applicable building requirements.