Plywood Calculator
How many sheets of plywood, OSB or sheathing you need: area of floors, walls or roofs, sheet size and extra for cuts, with cost.
Plywood, OSB and other sheathing are sold by the sheet, usually 4 × 8 ft (32 ft²) in the US and 2440 × 1220 mm (2.98 m²) in the UK, with 2400 × 1200 mm common in Australia. The count is the area to cover plus extra for cuts, divided by the area of a sheet. A 16 × 12 ft floor is 192 ft²; with 10% extra that's 211 ft², or 7 sheets of 4 × 8. Enter the floor, wall or roof areas (rectangles, triangles for gables, or a known area) and the calculator gives the sheets to buy and the cost.
- Sheets
- 7
- Area
- 192 ft²
- Sheet area
- 32 ft²
4 × 8 ft
211.2 ft² with extra
per sheet
How it was worked out
- Area: 16 ft × 12 ft = 192 ft²
- Plus 10% for cuts = 211.2 ft²
- 211.2 ft² ÷ 32 ft² per 4 × 8 ft sheet = 6.6, rounded up to 7 sheets
Works for plywood, OSB, particleboard flooring and sheathing. Lay floor and roof sheets with staggered joints across the joists or rafters, and use the thickness your span and code call for.
Common use cases
- Subfloor sheets for a room, shed or loft
- Roof decking or wall sheathing
- OSB for a garage or workshop wall
- Plywood for a project you've measured by area
How to use
- Choose your units.
- Enter each area; use Triangle for gable ends and Known area if you already have it.
- Choose the sheet size and extra for cuts, and a price per sheet if you like.
- Read the sheets needed.
FAQ
How many sheets of plywood do I need?
Area ÷ sheet area, with about 10% extra for cuts. A 4 × 8 ft sheet covers 32 ft², so 192 ft² needs 6 sheets before extra and 7 after.
What size is a sheet of plywood?
4 × 8 ft (1220 × 2440 mm) is the standard size in the US and UK. In Australia 2400 × 1200 mm is common. Longer sheets are made for some uses.
What thickness do I need?
It depends on the joist or rafter spacing, the load and what goes on top. Subfloors and roof decks have minimum thicknesses in building codes and in the sheet maker's span ratings, so check those.
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Results are estimates for planning and buying materials, worked out from the figures you enter and typical values (weights, coverage, sizes) that vary by product and supplier. They are not engineering, building or professional advice. Check your local building code, the product maker's instructions and your supplier's figures before you buy or build, and use a qualified professional for structural, electrical and gas work.