Subfloor Calculator
Count the sheets of subfloor plywood or OSB a room needs.
What you'll need to order
- 3/4 in tongue-and-groove plywood or OSB
- subfloor adhesive
- subfloor screws
Prices vary by region and haul distance. Get quotes from at least two local suppliers.
How this calculator works
sheets = area ÷ 32 × 1.10
A 4 by 8 sheet covers 32 sq ft. Lay sheets perpendicular to the joists and stagger the end joints between rows — running all joints in one line halves the floor stiffness.
Worked example
With room length 20 ft, room width 16 ft, joist spacing 16 in, this calculator returns 11 .
Waste allowance
The headline figure includes a 10% allowance for waste and over-ordering. The exact requirement is shown alongside it.
Frequently asked questions
How thick should a subfloor be?
Three-quarter inch tongue-and-groove over joists at 16 inch centres. At 24 inch spacing you need 7/8 or 1 inch, or the floor will feel springy between joists.
Plywood or OSB for a subfloor?
Both meet code and OSB costs less. Plywood dries out better after a wetting and holds fasteners slightly better at the edges, which matters if the deck will sit exposed during construction.
Should subfloor be glued as well as screwed?
Yes. Adhesive between joist and sheet is what eliminates squeaks — screws alone loosen as the lumber dries and shrinks. Use a proper subfloor adhesive, one tube per two sheets.
How far apart should subfloor screws be?
Six inches along the sheet edges and 12 inches through the field. That works out to roughly 50 screws per 4 by 8 sheet on joists at 16 inch centres.