Free tool
Plywood calculator for area, sheets and waste
How many sheets of plywood or OSB to buy for a floor, wall or roof. Measure in feet or metres, leave out openings you are not covering, set your own waste, and pick the sheet size.
Sheets to buy
7
192 sq ft to cover · 6.6 sheets with waste, rounded up
An area estimate, not a layout. It divides the area you enter by the area of a sheet and rounds up. Cuts, stagger, openings and roof geometry change the real count, so check it against a sheet layout before ordering. It does not choose a thickness, grade or span rating.
The arithmetic, in full
Area. Area = length × width × the number of surfaces, less openings. A 12 × 16 ft floor is 192 sq ft.
Sheets. Sheets = area × (1 + waste ÷ 100) ÷ one sheet's area, rounded up. At 10% waste that floor is 192 × 1.1 ÷ 32 = 6.6, so 7 sheets.
A roof. Two roof planes, each 30 × 14 ft, at 10% waste: 840 sq ft, 28.875 sheets, so 29. Hips, valleys and overhangs are not in that number; they are why roofs usually need more waste than floors.
Metric. A 5 × 4 m floor is 20 m². A 1220 × 2440 mm sheet is 2.9768 m², so 6.719 sheets with no waste, rounded up to 7.
What each input means
- Length and width
- Of each surface to cover, in feet or metres. For a roof, measure along the slope, not the plan: the roof pitch calculator converts a horizontal run into a slope length.
- Surfaces
- How many of that size: two identical roof planes, four identical walls.
- Openings
- Total area you will leave uncovered, in square feet or square metres. Leave blank if you sheathe over openings and cut them out.
- Waste
- Your allowance for offcuts and damage, as a percent of the area. Negative values are treated as zero.
- Sheet size
- 4 × 8 ft is the common North American sheet; 1220 × 2440 mm is its metric size. 4 × 9 and 4 × 10 ft suit taller walls.
Frequently asked questions
- How many sheets of plywood do I need?
- Take the area to cover, subtract any openings you are leaving out, add your waste allowance, and divide by the area of one sheet. Round up, because a part sheet is still a sheet you buy. A 4 × 8 ft sheet covers 32 sq ft; a 1220 × 2440 mm sheet covers about 2.98 m².
- How much waste should I allow?
- It depends on the layout, which is why it is an input. A plain rectangular floor with staggered joints wastes little; a roof with hips and valleys, or a wall with many openings, wastes much more because offcuts often cannot be reused. The calculator starts at 10%; change it to what your own jobs have taught you.
- Should I subtract windows and doors?
- Only if you are not sheathing over them. Many crews sheathe straight across openings and cut them out, in which case the cut-out is waste rather than a saving. Enter openings only for the area you will genuinely leave uncovered.
- Is this accurate enough to order from?
- It is an area estimate. The real count moves with the layout: sheet stagger, cut-offs, openings and roof geometry. For anything beyond a simple rectangle, a drawn sheet layout is more reliable, and an estimator should check the number before it goes on an order.
- Does it tell me what thickness or grade to use?
- No. Thickness, grade, span rating and fastening come from your drawings, the manufacturer and the building code. This tool only counts sheets.
Getting it into a priced estimate
Enter the sheet count as a material line on the estimate with your supplier's price. Every quantity and rate on a BuildersBridge estimate stays editable, so a changed layout is an edit, not a new quote.
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