Roof Sheathing Calculator

Find How Many Sheets of Plywood You Need to Sheath a Roof

Sheathing adds structure and stability to your roof. The sheath is a layer of plywood – usually sheathing or structural plywood – that is applied to the frame of the roof.

It can be made of different materials, from fir and pine to OSB, and gives a stable surface for your roofing to adhere to. All types of sheathing plywood come in sheets that measure 4′ x 8′ nominally.

To find the amount of plywood needed to cover a roof, start by finding the area of the roof. Once the area is known, divide it by the area of a 4×8 sheet to find how much sheathing is needed.

Find the Area of a Roof

Multiply the length of each section of the roof in feet by the width of the section to find the area for that section in square feet. If you have multiple sections of roof, find the area of each and add them together to find the total area.

If your roof is not flat and you cannot climb to the peak to get accurate width measurements, then you can add a multiplier for the pitch of your roof.

Use our roof pitch calculator to find the pitch of your roof or find the pitch multiplier, then multiply the area of the footprint of your roof by the multiplier to find the actual area.

Alternatively, find the area of your roof using our roofing calculator, which can also estimate shingles and material needed for your project.

If your roof has triangles and other shapes, you’ll need to use a calculator to find the square footage.

Keep in mind that different roof shapes will have different square footages, regardless of the home size. A hipped roof will be nearly twice as large as a gable roof, even if both are on a home of the same square footage.

Calculate Sheathing Needed

Once you have the size of the roof area, you can divide it by the area of a sheet of plywood to find the number of sheets needed. A 4×8 sheet of plywood is 32 sq ft. So, dividing the area of the roof by 32 will give you the number of sheets needed.

It’s usually a good idea to get an extra few sheets of plywood when ordering to allow for waste and off-cuts. Small scraps are often unusable to span joists and effectively cover the roof, so extra material will save extra trips to the hardware store.