Plywood Calculator
Work out how many sheets of plywood or OSB you need for a floor, wall or roof — with sheet size options, a realistic waste factor and cost per sheet.
Large windows, stairwells, garage doors
—
You might also need:Board Foot Calculator·Stud Calculator
Sheet count math
standard 4 × 8 sheet = 32 sq ft
A 24 × 12 ft subfloor is 288 sq ft — nine sheets exactly, ten with 10% waste. Always round up: half a sheet short mid-job means a trip to the yard, and sheet goods rarely cut down to exactly what's left over.
Plywood thickness by application
| Application | Thickness | Notes |
|---|---|---|
| Subfloor (16″ o.c. joists) | ¾″ T&G | Glue and screw to stop squeaks |
| Subfloor (24″ o.c.) | 1⅛″ | Or add sleepers/blocking |
| Wall sheathing | ⅜–½″ | OSB is the budget equivalent |
| Roof sheathing | ½–⅝″ | ⅝″ for 24″ rafter spacing |
| Cabinets / shelving | ¾″ hardwood ply | Birch or maple face |
| Underlayment | ¼″ | Smooths subfloor for vinyl/tile |
Working with sheet goods
- Stagger the seams: never line up panel joints in a continuous line — offset each row by at least one joist or stud bay.
- Leave expansion gaps: ⅛ inch between sheets on floors and roofs, or panels buckle when they swell.
- Buy one spare: the cost of one extra sheet is less than a second trip.
- Framing underneath: stud calculator for walls, rafter calculator for roofs. Finishing over it? Drywall and flooring calculators.
Frequently asked questions
How many square feet is a sheet of plywood?+
A standard 4 × 8 ft sheet is 32 square feet. Less common sizes: 4 × 9 is 36 sq ft, 4 × 10 is 40 sq ft, and 5 × 5 Baltic birch is 25 sq ft. Divide your area by 32 and round up for the usual case.
How many sheets of plywood do I need for a 12x12 room?+
A 12 × 12 ft floor is 144 square feet — five 4 × 8 sheets exactly, or six with a waste allowance. Subfloor jobs waste less than roofs and walls because there are fewer angled cuts.
What thickness of plywood should I use?+
Subfloors: ¾ inch tongue-and-groove over joists at 16 inches on center. Wall sheathing: ⅜–½ inch (or OSB). Roof sheathing: ½–⅝ inch depending on rafter spacing. Cabinets and furniture: ¾ inch hardwood ply. Thinner than spec means bounce and sag.
Is OSB or plywood better?+
For sheathing and subfloor, OSB is 20–30% cheaper and structurally equivalent to code. Plywood handles moisture better (it dries faster and doesn't swell permanently at cut edges) and holds fasteners better. Many builders use OSB on walls and plywood where water risk is higher.
How much waste should I add for plywood?+
Add 10% for simple rectangular floors and walls, 15% for roofs with hips and valleys or rooms with many obstructions. Sheet goods waste in whole-panel chunks, so one awkward cut can cost a full sheet.