How it works
Area, sheet size, allowance — three inputs and a count.
Measure the area
Length and width of the floor, wall or roof deck you are sheathing.
Confirm the sheet
4 × 8 is standard. Change it if you are buying 4 × 9 or 5 × 5 sheets.
Get the sheet count
Square footage, sheet area, and how many to load on the truck.
An area count, not a cutting plan
A standard sheet is 4 by 8 feet, which is 32 square feet. Divide your area by 32, add an allowance, round up, and you have the number of sheets. For a 20 by 14 foot floor that is 280 ft², or ten sheets with 10% waste.
The honest caveat is that this is a floor, not a ceiling. Sheets only divide cleanly into a room when the room happens to be a multiple of 4 and 8 feet, and rooms rarely are. Every partial sheet at the edge leaves an offcut, and whether that offcut is usable depends on where the next cut falls.
Two rules push the real count above the arithmetic. Joints must land on framing — every sheet edge needs a joist, stud or rafter under it, which sometimes means cutting a sheet narrower than the leftover space. And joints should be staggered, so adjacent rows do not line up, which means starting alternate rows with a half sheet. Both cost material.
That is why 10% is the working figure rather than 5%. On a simple rectangle you may beat it; on anything with an angle, a stairwell or a chimney chase, plan on more.
Frequently asked questions
How many square feet in a sheet of plywood?
32 square feet for a standard 4 × 8 sheet.
How many sheets for a 20x14 floor?
Ten sheets of 4 × 8, including a 10% allowance for cuts and staggering.
Is OSB the same size as plywood?
Yes, OSB comes in the same 4 × 8 sheets, so the count is identical. The thickness and price differ, not the coverage.
Why add 10% waste?
Because sheet edges have to land on framing and joints should be staggered between rows. Both force cuts that leave unusable offcuts.
More material calculators
Estimates are for planning only. Confirm quantities with your supplier before ordering.