Plywood & OSB Sheet Calculator
Find how many sheets of plywood or OSB you need for a subfloor, wall sheathing, or roof deck. Enter the area, pick a sheet size, and the calculator adds waste and rounds up to whole sheets.
How to use this calculator
- Measure the area length and width in feet (the floor, wall, or roof plane).
- Pick the sheet size you are buying; 4 × 8 ft (32 sq ft) is standard.
- Choose a waste allowance — more cuts and openings mean more waste.
- For roof or subfloor, stagger the seams; the waste allowance covers the offcuts that creates.
The formula
Sheet goods are sized by area, so we divide the area to cover by the area of one sheet.
Sheets = area × (1 + waste %) ÷ sheet area. A 4 × 8 sheet is 32 sq ft.
Round up to whole sheets — you cannot buy a partial sheet.
Worked example
A 24 ft × 20 ft subfloor with 4 × 8 sheets and 10% waste.
Area = 24 × 20 = 480 sq ftWith 10% waste = 528 sq ftSheets = 528 ÷ 32 = 16.5 → 17 sheets
A 480 sq ft subfloor needs about 17 sheets of 4 × 8 plywood.
Frequently asked questions
How many 4x8 sheets do I need?
Each 4 × 8 sheet covers 32 sq ft. Divide your area by 32 and add 10% for waste. A 480 sq ft area needs about 17 sheets.
What thickness of plywood for a subfloor?
For a subfloor over joists 16 inches on center, 3/4 inch tongue-and-groove plywood or OSB is standard. Wider joist spacing needs thicker sheathing.
Plywood or OSB?
OSB is cheaper and fine for most sheathing and subfloor. Plywood is lighter, handles moisture and repeated wetting better, and holds fasteners slightly better at edges.