Plywood Calculator — How Many Sheets of Plywood or OSB

How to use the plywood calculator

Enter the length and width of each area in feet; use How many for repeats like identical walls.
Pick the sheet size and a waste allowance.
Subtract the area of doors and windows if you are sheathing walls.

The formula

Sheets = area (sq ft) ÷ sheet area × (1 + waste), rounded up

The drawing shows the first area laid with staggered joints, as sheathing should be. For roof planes, find the slope length with the rafter calculator.

Frequently asked questions

How many sheets of plywood do I need?

Work out the area in square feet, divide by 32 (the area of a 4 × 8 sheet) and add about 10% for cuts. A 16 × 12 ft floor is 192 sq ft: 192 ÷ 32 = 6 sheets, 7 with waste.

How much area does a sheet of plywood cover?

A 4 × 8 sheet covers 32 sq ft, 4 × 9 covers 36 and 4 × 10 covers 40.

How do I count plywood for a roof?

Measure each roof plane along the slope (eave to ridge) and along the eave, and enter each plane as an area. If you only know the building footprint, multiply by the rafter factor for your pitch — the roof pitch calculator shows it.

How much waste should I allow?

About 10% for floors and simple walls, 15% or more for roofs with hips and valleys or walls with many openings.