How to measure for siding
- Walls: width × height of each rectangular wall, eave to foundation.
- Gables: the triangles under a gable roof: base × peak height ÷ 2.
- Subtract openings: width × height of windows and doors (or use 15 sq ft per window and 21 per door).
- Add waste: 10% for simple rectangular houses, 15% or more with many corners, gables and dormers.
- Divide by 100 for squares — siding is priced and sold by the square.
squares = (walls + gables − openings) × (1 + waste) ÷ 100
Coverage by siding type
| Siding | Coverage per piece | Pieces per square |
|---|---|---|
| Vinyl, double 4" (12′6″ panel) | 8.33 sq ft | 12 (box of 24 = 2 sq) |
| Vinyl, double 5" (12′6″ panel) | 10.42 sq ft | 9.6 (box of 20 = 2.1 sq) |
| Fiber cement lap, 8¼" plank, 7" exposure (12′) | 7 sq ft | 14.3 |
| Engineered wood lap, 8" plank, 7" exposure (16′) | 9.33 sq ft | 10.7 |
| 4×8 sheet siding (T1-11, panel) | 32 sq ft | 3.1 |
Coverage depends on the exposure (the visible face once lapped), not the full board width — a 8¼" fiber cement plank shows only 7".
Don't forget trim and accessories
- Starter strip: the perimeter length of all walls.
- J-channel: around every window and door (perimeter of each opening) and along rakes and soffits.
- Corner posts: one per outside and inside corner, as tall as the wall.
- House wrap: same area as the walls plus 10% for laps.
FAQ
How many squares of siding for a 2,000 sq ft house?
Floor area isn't wall area. A two-story 2,000 sq ft house (about 25 × 40 ft footprint) with 18 ft of wall has roughly 2,340 sq ft of wall plus gables; after openings and 10% waste that's typically 22–26 squares.
How many square feet are in a box of vinyl siding?
Most boxes hold 2 squares (200 sq ft): 24 double-4" or 20 double-5" panels of 12′6″.
Should I subtract windows when ordering siding?
Subtract large openings like garage doors and patio doors. Many installers don't subtract small windows — the offcuts get used elsewhere — so subtracting all openings and adding 10–15% waste lands close to their numbers.