Plywood & Sheathing Calculator
Follow your plans and the panel maker's instructions for sheet direction, gaps and the thickness your joist or rafter spacing needs.
How the plywood & sheathing calculation works
Measure the area
A 24 × 16 ft floor is 384 sq ft. Subtract big openings like stairwells; leave small ones in, since you'll cut them out of full sheets.
For a roof, add the slope
Multiply the footprint by √(1 + (pitch ÷ 12)²). At 6/12 that's 1.118, so a 384 sq ft footprint has about 429 sq ft of roof.
Divide by the sheet size
A 4 × 8 sheet covers 32 sq ft. 384 ÷ 32 is exactly 12 sheets before waste.
Add waste and round up
10% extra makes 13.2, so buy 14 sheets. At $40 a sheet that's $560.
Worked example. A 24 × 16 ft floor is 384 sq ft, or 12 sheets of 4 × 8 plywood. With 10% for waste, buy 14 sheets, $560 at $40 each. The same footprint as a 6/12 roof is about 429 sq ft and needs 15 sheets.
Plywood & Sheathing FAQ
How many sheets of plywood do I need?
Divide the area in square feet by 32 for 4 × 8 sheets, add about 10% for cuts and waste, and round up. 384 sq ft needs 12 sheets before waste and 14 with it.
How many square feet are in a sheet of plywood?
A 4 × 8 sheet is 32 sq ft (4 × 8 = 32), 4 × 9 covers 36, 4 × 10 covers 40 and 4 × 12 covers 48.
How do I calculate roof sheathing?
Multiply the building footprint (with overhangs) by the slope factor for your pitch, √(1 + (pitch ÷ 12)²), then divide by the sheet area. A 6/12 pitch adds about 12%.
Should I use plywood or OSB?
Both come in the same sheet sizes, so the count is the same. Choose by your plans, local code and price; use the price field to compare.
How much waste should I allow?
About 10% for simple floors, walls and gable roofs. Allow more for hips, valleys, dormers and rooms with many corners.
How many sheets of plywood do I need for a roof?
Take the footprint with overhangs, multiply by the slope factor and divide by 32 for 4 × 8 sheets. A 24 × 16 ft footprint at 6/12 is about 429 sq ft, or 13.42 sheets; with 10% waste, buy 15.
How much does a sheet of plywood weigh?
It depends on the thickness, the wood species and whether it's plywood or OSB, so check the manufacturer's spec sheet or the store listing. Weight doesn't change the sheet count, but it matters when you carry sheets up to a roof.
Why is my sheet slightly smaller than 4 × 8 ft?
APA says panels marked "Sized for Spacing" are made a little under the nominal 48 × 96 in so you can leave the gaps the maker recommends. Count them as full 4 × 8 sheets; the difference doesn't change how many you buy.
Sources: APA – The Engineered Wood Association: Plywood (incl. Sized for Spacing)