Subfloor Calculator
Subfloor panels are 4×8 sheets of OSB (Oriented Strand Board) or plywood installed over floor joists to create the structural floor deck. Standard residential subfloor is 3/4" OSB over 16" OC joists — the most common and cost-effective choice. Plywood is stronger and more moisture-resistant and is preferred in bathrooms, kitchens, and crawlspace applications. Enter your floor dimensions to get 4×8 panel count with 10% waste (for cuts and panel layout), tubes of construction adhesive (applied to joist tops before panel installation to eliminate squeaking), and pounds of 1-5/8" subfloor screws. Glue-nail installation (applying adhesive and screwing — not just nailing) is the best practice and dramatically reduces floor squeaks. Panels must be installed with staggered joints and 1/8" gaps at all edges to allow for expansion.
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Top Pick3/4" OSB Subfloor (4×8) — Home Depot~$34/sheet* Affiliate links — we may earn a commission at no cost to you.
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How to Use This Calculator
- 1Enter your measurements in the fields above. Use the units shown next to each field (ft, in, etc.).
- 2Click Calculate to get your material estimate instantly.
- 3Review the highlighted result — it shows the key quantity you need to order.
- 4Use Copy Results to save your estimate, or bookmark the URL — your inputs are encoded in the link.
Pro tip: Always add 10% to your material order to account for waste, cuts, and defects.
Frequently Asked Questions
How many sheets of subfloor do I need for a 20×15 room?
A 20×15 room is 300 sq ft. Each 4×8 panel covers 32 sq ft. With 10% waste, you need 300 × 1.1 / 32 = 10.3, so 11 panels.
Should I use OSB or plywood for subfloor?
OSB is the industry standard for subfloor — it's stronger than plywood of the same thickness, cheaper, and performs well when properly installed and kept dry. Use plywood in areas with high moisture exposure (crawl spaces, bathrooms) or when installing a tile floor that requires extra rigidity.
What thickness subfloor do I need?
Use 3/4" (23/32") OSB or plywood for 16" OC joists — this is the standard residential specification. For 19.2" OC joists, use 5/8" or 3/4". For 24" OC joists, use 7/8" or 1-1/8" panels. Installing tile? Use 3/4" subfloor plus 1/4" cement backer board for a total rigid assembly.
Do I need to glue subfloor panels?
Gluing is not always required by code but is strongly recommended. Construction adhesive applied to the top of each joist before fastening the panel bonds the subfloor to the joists, dramatically reducing floor squeaks. Use a construction adhesive rated for subfloor (like PL Premium or Loctite PL400) and supplement with screws — not nails alone — for the best result.