Plywood and sheathing calculator

How plywood sheets are calculated

Sheathing is ordered by the sheet, so the calculator finds the area to cover, adds a waste allowance for cuts, and divides by the area one sheet covers. A part sheet still means buying a whole one, so the count always rounds up.

Sheet coverage is 32 ft² for a 4 × 8, 40 ft² for a 4 × 10 and 48 ft² for a 4 × 12. Fasteners and roof clips follow from the sheet count:

The 50-per-sheet figure comes from nailing 6 in apart along the panel edges and 12 in apart along the framing in the middle of the sheet, the spacing IRC Table R602.3(1) gives for wall and floor sheathing. The 2021 IRC requires 6 in in the field on roof sheathing as well; across rafters at 24 in oc that is about 45 nails per sheet, so 50 still covers it, but rafters at 16 in oc take about 63. Use the Or area field when you already know an area, for example a roof surface from the roof area calculator, which includes the pitch. That area's length and width are then ignored. For several walls, roof planes or floors, use “+ Add another area”: the areas are added together before waste is applied, so the sheets are rounded once for the whole job.

Worked example: 40' × 30' subfloor

The calculator opens on a 40' × 30' subfloor with 4 × 8 sheets and 10% waste.

1. Area: 40 × 30 = 1,200 ft².
2. Add waste: 1,200 × 1.10 = 1,320 ft².
3. Sheets: 1,320 ÷ 32 = 41.25, rounded up to 42 sheets.
4. Fasteners: 42 × 50 = 2,100 nails, or about 21 lb of 8d nails.
5. H-clips: none, because this is a subfloor. The same area as a roof deck would need 42 × 4 = 168 clips.

Laying out and fastening the sheets

• Run the long edge of each sheet across the joists, studs or rafters. Panels are stiffer along their length, and their span rating assumes this direction.
• Stagger the end joints by half a sheet from row to row, as the diagram shows, so no two rows break on the same joist or rafter. Every end joint should land on framing.
• Start each row with the factory edge on the straight line you snap, and put the cut edges at the walls, eaves or ridge where trim or the next layer covers them.
• Leave about 1/8 in between sheets at ends and edges so panels can swell without buckling. Tongue-and-groove panels build the gap into the long edges, but the ends still need it.
• For subfloors, glue to the joists as well as nailing or screwing. It stiffens the floor and cuts down on squeaks.
• Walls: the width field is the wall height. Enter each wall as its own area with “+ Add another area”, and each gable triangle (half the base times the height) in its own Or area field, and keep the waste at 10% or higher when there are many window and door cutouts.

Roof decks and H-clips

On a roof, measure the sloped surface, not the footprint. The roof area calculator applies the pitch factor and gives you the number to enter here. Raise the waste to 15% for hip roofs, valleys and dormers. The calculator flags anything lower on a roof.

Where the long edges of two sheets meet between rafters, an H-clip keeps one edge from deflecting more than the other under a load. APA guidance calls for this edge support where the panel's span rating requires it, which covers many common roof panels on 24 in oc framing; tongue-and-groove edges or blocking do the same job. Check the span rating stamped on the panel (for example 24/16) against your rafter spacing. Steep, high or large roofs are a job for a crew with fall protection.