How many pieces of siding are in a box? Usually 24, 22 or 20, depending on the profile, and all three cartons cover the same two squares. The piece count changes and the coverage does not, because a carton of vinyl siding is built to 200 square feet and then filled with however many panels that takes.
That is the short answer. The reason published answers to this question range from 10 pieces to 25 is that almost none of them say what exposure they are talking about, and the exposure is the only number that decides it.
A panel does not cover its own width
Siding laps. Every course hides the top of the course below it, along with the nail hem it is fastened through and the lock it clips into. What shows when the wall is finished is the exposure, and it is always less than the panel you carried up the ladder.
How much less is not a rounding error. Two retail listings for ordinary Double 4 vinyl, both 24 panels to the carton, describe the same panel as 8 inches wide and as 9.23 inches wide. One is quoting the exposure and the other is quoting the physical panel. They disagree by 15 percent on the width and agree exactly on the coverage, which tells you which number the carton was designed around.
The name carries the exposure
Vinyl profiles are named for what they expose. Double 4 is two courses of 4 inches on one panel, so the panel covers 8 inches. Double 5 covers 10. Triple 3 covers 9. The name is the specification, and it is usually the only place the exposure appears, because neither of the listings above states an exposure or a coverage anywhere on the page.
Once you have the exposure, the rest is one line:
Pieces in a square
100 ÷ [ ( exposure in inches ÷ 12 ) × length in feet ]
The bracket is what one piece covers · exposure is what shows after the lap, not the width on the listing · a square is 100 sq ft
A Double 4 panel 12 feet 6 inches long covers 8 ÷ 12 × 12.5, which is 8.33 square feet. A square is 100 square feet, so it takes 12 panels, and a two square carton holds 24 of them.
How many pieces of siding are in a box: three real cartons
These are three products off the same shelf. The listed width row is what the listing prints; the exposure row is what the wall actually gets.
| Double 4 lap | Double 4.5 Dutch lap | Double 5 Dutch lap | |
|---|---|---|---|
| Listed width | 9.23 in | 10.21 in | 11.22 in |
| Exposure | 8 in | 9 in | 10 in |
| Length | 150 in | 145 in | 144 in |
| Pieces per carton | 24 | 22 | 20 |
| One piece covers | 8.33 sq ft | 9.06 sq ft | 10 sq ft |
| Pieces in a square | 12 | 11 | 10 |
| Carton covers | 200 sq ft | 199 sq ft | 200 sq ft |
Twenty four pieces, twenty two, twenty. Twelve to a square, eleven, ten. And every carton lands within a square foot of two squares. The piece count is the output of the design, not the point of it.
Length moves it too, which is worth seeing once. The Double 5 above is 144 inches long and gives exactly 10 pieces to a square. The same Double 5 profile in a 12 foot 6 inch panel covers 10.42 square feet a piece and gives 9.6. Same name, same exposure, different answer, because the count was never a property of the profile.
What the listed width costs you
Run the same three cartons using the width printed on the listing instead of the exposure and every one of them looks bigger than it is:
- Double 4 at 9.23 inches: 231 square feet a carton instead of 200, over by 15 percent
- Double 4.5 at 10.21 inches: 226 instead of 199, over by 13 percent
- Double 5 at 11.22 inches: 224 instead of 200, over by 12 percent
Twelve percent does not sound like a problem until it crosses a carton. On a wall needing 2,400 square feet of siding, the right figure orders 12 cartons and the listed width orders 11. That missing carton is 200 square feet, which is roughly two courses all the way around a house, and you find out about it on the last afternoon.
Fiber cement is where the teens come from
Published answers in the teens and twenties are not wrong, they are just about a different material. Fiber cement is sold as single planks rather than double panels, so one piece carries one course and covers much less.
James Hardie requires a minimum overlap of 1.25 inches between courses, which sets the exposure at the plank width less 1.25. An 8.25 inch plank runs at 7 inches, a 7.25 inch plank at 6, a 5.25 inch plank at 4. On a 12 foot length that is 7, 6 and 4 square feet a plank, so a square takes about 14, 17 and 25 pieces respectively.
So “10 to 12 pieces a square” and “14 to 20 pieces a square” are both true statements about siding, and neither is useful without knowing which product is being described. That is the whole disagreement.
Going the other way, from a wall to a carton count
Take a 30 by 40 house with nine foot walls. That is 140 feet of wall run and 1,260 square feet gross. Two doors and ten windows take out about 192, leaving 1,068 square feet to cover. Add the 10 percent that CertainTeed suggests for siding, soffit and accessories and the order is 1,174.8 square feet, which is 11.75 squares.
Cartons come in two squares, so that is six cartons and 12 squares bought. Six cartons of Double 5 is 120 panels and six of Double 4 is 144, against the 118 and 141 the wall itself needs. Same wall, same coverage, twenty four more pieces to carry up the ladder in Double 4.
The 132 square feet left over is not waste on top of the waste allowance, it is the allowance plus the rounding to whole cartons. Keep it. Vinyl fades, and a panel from the same run is the only thing that will ever match the wall it is repairing.
What the carton count leaves out
None of the accessories are sold by the square, and they are the usual reason for a second trip:
- Starter strip, one run along the foot of every wall
- Utility trim, closing the top course under the eave, so the same run again
- Corner posts, the number of outside corners times the wall height
- J channel, all four sides of every window and door
- Soffit and fascia, counted separately and often the larger order
On that 30 by 40 house it comes to 140 feet of starter, 140 feet of utility trim, 36 feet of corner post and 200 feet of J channel. The J channel is the one that surprises people, because ten windows at four sides each adds up faster than the wall does.
Work out your own carton count
Frequently asked
Usually 24, 22 or 20, depending on the profile. Cartons are built to cover two squares, or 200 square feet, and hold however many panels that takes: 24 pieces of Double 4, 22 of Double 4.5 Dutch lap, 20 of Double 5 Dutch lap. The piece count is the result, the coverage is the specification.
Divide 100 square feet by the coverage of one piece, which is the exposure in inches divided by 12, times the length in feet. For the three cartons above that is 12 pieces for Double 4, 11 for Double 4.5 and 10 for Double 5. Length moves it: the same Double 5 profile in a 12 foot 6 inch panel gives 9.6. Use the exposure, not the width on the listing, which includes the nail hem and the lock.
Two squares, which is 200 square feet, for almost every standard carton. That figure holds across profiles even though the piece count changes, because the carton is designed around the coverage. A few products are packed as a single square, so check the carton rather than assuming.
About 14.3. An 8.25 inch plank is hung at 7 inches of exposure, because James Hardie requires a minimum 1.25 inch overlap, so a 12 foot plank covers 7 square feet and a square takes 100 divided by 7. A 7.25 inch plank at 6 inches of exposure takes about 17 pieces.
Work out the wall area, subtract the openings, add a waste allowance and divide by 200. A 30 by 40 house with nine foot walls is 1,260 square feet gross and about 1,068 after two doors and ten windows, which at 10 percent waste is 11.75 squares, so six cartons.