A one-story house of 40 × 28 ft with 9 ft walls and two 6/12 gable ends has 1,260 sq ft of wall to side once ten windows and two doors are taken out. Siding is sold by the square, 100 sq ft, so that is 12.6 squares, and with 10% for waste you order 13.9 squares. In 8¼ in HardiePlank that is 198 planks.
How the siding calculator works
Every wall is a rectangle and every gable end is a triangle. The calculator adds them up, subtracts the openings, adds your waste allowance and divides by what one piece covers.
squares = (walls + gables − windows − doors) × (1 + waste) ÷ 100 sq ft
pieces = order area ÷ (piece length × exposure)
The walls come from the perimeter times the wall height, or wall by wall if your house has different heights. A gable end is half its width times its rise: ½ × 28 ft × 7 ft = 98 sq ft. If you know the roof pitch instead of the rise, the rise is half the width times pitch ÷ 12, so a 28 ft gable at 6/12 rises 7 ft. The roof pitch calculator finds the pitch from two measurements if you do not know it.
Worked example: the default house
| Part | Math | Area |
|---|---|---|
| Walls | 136 ft perimeter × 9 ft | 1,224 sq ft |
| Gable ends | 2 × ½ × 28 ft × 7 ft | 196 sq ft |
| Windows | 10 × 36 in × 48 in | −120 sq ft |
| Doors | 2 × 36 in × 80 in | −40 sq ft |
| Net wall | 1,260 sq ft | |
| With 10% waste | 1,260 × 1.1 | 1,386 sq ft, 13.86 squares |
An 8¼ in HardiePlank is 12 ft long and shows 7 in to the weather, so one plank covers 12 ft × 7 in = 7 sq ft. 1,386 ÷ 7 = 198 planks. The same house takes 167 panels (7 cartons) of double 4 in vinyl, 152 boards of 8 in LP SmartSide, or 40 bundles of 16 in cedar shingles.
Exposure is what changes the count
The piece count depends on the exposure (the reveal), not the board's width. Lap siding overlaps the course below, so part of every board is hidden.
| Siding | Piece | Exposure | One piece covers |
|---|---|---|---|
| HardiePlank 6¼ in | 12 ft | 5 in | 5 sq ft |
| HardiePlank 8¼ in | 12 ft | 7 in | 7 sq ft |
| HardiePlank 12 in | 12 ft | 10¾ in | 10.75 sq ft |
| LP SmartSide 8 in | 16 ft | 6⅞ in | 9.17 sq ft |
| Vinyl double 4 in | 12 ft 6 in | 8 in | 8.33 sq ft |
| Vinyl double 5 in | 12 ft | 10 in | 10 sq ft |
| Cedar shingles 16 in | bundle | 7 in | 35 sq ft |
James Hardie makes HardiePlank in 12 ft lengths, 5¼ to 12 in wide, for exposures of 4 to 10¾ in, and its gable instructions mark a 1¼ in course overlap. LP's coverage chart lists reveals of 4⅞, 6⅞ and 10⅞ in on 16 ft boards, and its application instructions require at least 1 in of overlap. The Cedar Shake & Shingle Bureau limits single-course sidewall exposure to 7 in for 16 in shingles and 8 in for 18 in shingles, and at 7 in a four-bundle square covers 140 sq ft. Vinyl panels come 2 squares to a carton in the Mastic specification guide: 24 double 4 in panels or 20 double 5 in panels.
Gable ends
Gables are where most siding estimates go wrong, because the triangle is easy to forget and every course gets an angled cut. Count each gable end once, even if both ends of the house match: the calculator multiplies by the count. On a hip roof there are no gable ends, so set the count to 0. Dormers are small gables too: add them with their own width and rise, or add their area as a separate wall.
By square footage
If a contractor's plan or an old invoice already gives the siding area, switch to By square footage and type it in. The calculator then gives squares, pieces, cartons and nails. Starter, J-channel and corner posts need the house outline, so they only appear in the other two modes.
Trim, starter and nails
The material list adds what goes with the siding:
- Starter runs around the whole base of the house, 136 ft here. HardiePlank starter is ripped from planks in 1¼ in strips; an 8¼ in plank gives six strips, so two extra planks cover 136 ft.
- Trim around openings goes up both sides and across the head of every window and door, plus both rakes of each gable: 205 ft on the default house.
- Corner trim or posts is one wall height per corner, 36 ft for four 9 ft corners.
- Nails for lap boards go in at every stud, 16 in on center, so a 12 ft plank takes 9 nails and 198 planks take 1,782. For vinyl the Vinyl Siding Institute estimates 0.01 lb of roofing nails per sq ft.
Waste allowance
10% suits a plain rectangle with two gables. Add 5% for a house with many corners, dormers or a steep roof, since every gable course is cut on an angle. The Vinyl Siding Institute notes that most installers do not subtract ordinary windows at all and keep that area as their allowance; subtracting them as this calculator does and then adding 10% is the tighter approach.
Next steps
- Siding with vinyl? The vinyl siding calculator counts cartons, J-channel, corner posts, soffit and fascia.
- To budget the job, the vinyl siding cost calculator prices materials, labor and tear-off for your state.
- Painting fiber cement or wood after it goes up? The exterior paint calculator turns the same wall area into gallons.
- Doing the roof at the same time? The roofing calculator sizes shingles for the same house.
- More tools for the outside of the house are on the roofing and siding calculators page.