Roof sheathing calculator
A roof is bigger than the house it covers, for two reasons the calculator handles for you:
- Overhangs. Add the eave and rake overhang to every side of the footprint. A 40 × 28 ft house with 1 ft overhangs is a 42 × 30 ft plan.
- Pitch. A sloped roof is longer than its plan. Multiply by √(1 + (rise ÷ 12)²): 1.118 for a 6/12 roof, 1.414 for 12/12.
| Pitch | Multiplier | 1,000 sq ft plan | 1,500 sq ft plan | 2,000 sq ft plan | 2,500 sq ft plan |
|---|---|---|---|---|---|
| 3/12 | 1.031 | 36 sheets | 54 | 71 | 89 |
| 4/12 | 1.054 | 37 | 55 | 73 | 91 |
| 5/12 | 1.083 | 38 | 56 | 75 | 94 |
| 6/12 | 1.118 | 39 | 58 | 77 | 97 |
| 7/12 | 1.158 | 40 | 60 | 80 | 100 |
| 8/12 | 1.202 | 42 | 62 | 83 | 104 |
| 9/12 | 1.250 | 43 | 65 | 86 | 108 |
| 10/12 | 1.302 | 45 | 68 | 90 | 112 |
| 12/12 | 1.414 | 49 | 73 | 98 | 122 |
Plan area includes overhangs; sheet counts are 4×8 with 10% waste. Use 15% for hip roofs, valleys and dormers, where more of each sheet ends up as offcuts. Not sure of your pitch? The roof pitch calculator works it out from a rise and run.
Roof plywood calculator: thickness, clips and nails
| Support spacing | Roof | Walls | Subfloor (tongue-and-groove) |
|---|---|---|---|
| 16 in o.c. | 7/16 in OSB or 15/32 in plywood | 7/16 in OSB or 15/32 in plywood | 19/32 in |
| 24 in o.c. | 7/16 in rated 24/16 with panel clips | 7/16 in rated 24/16 | 23/32 in |
On 24 in rafters or trusses, APA requires the unsupported long edges of 7/16 in panels to be supported, which is what panel clips (H-clips) are for — about one between each pair of rafters, so roughly four per sheet. The calculator adds them automatically when you choose 24 in spacing.
Nails come from the IRC fastening schedule: 8d nails every 6 in along supported panel ends and every 12 in on the intermediate rafters or studs. That's about 33 nails per sheet on 24 in framing and 43 on 16 in. Leave a 1/8 in gap at every panel edge and end; panels swell when they get wet, and without the gap the roof ripples under the shingles.
Wall sheathing and subfloor sheets
Walls: total wall length × height, plus the two gable triangles if you're sheathing them, minus about 21 sq ft per door and 15 sq ft per window. In practice many framers sheathe straight over the openings and cut them out afterward, so if you do that, set doors and windows to zero.
Subfloors: length × width ÷ 32 plus 10%, in tongue-and-groove panels glued and screwed to the joists. The calculator adds about one large tube of subfloor adhesive per two sheets.
Run every sheet with its long edge across the framing and stagger the end joints so they don't line up on the same rafter or joist. Then head to the roofing calculator for shingles and underlayment, or back to the stud calculator if the walls aren't framed yet.
