Siding for a 30 x 40 House
Siding needed
15.6 squares
140 ft perimeter, 9 ft walls, two 30 ft gables at 6/12, 10 windows, 2 doors, 12% waste.
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How that number is worked out
These are the figures this page was built with and every line the calculator produces from them. Change anything above and all of it moves.
- Wall perimeter140 ft
- Wall height to the eave9 ft
- Gable ends2 each
- Gable width30 ft
- Roof pitch, rise per 12 in6 /12
- Windows10 each
- Doors2 each
- Outside corners4 each
- Waste allowance12 %
Siding needed15.6 squares
| Wall area | 1,260 sq ft |
|---|---|
| Gable area | 225 sq ft2 gables at 6/12 |
| Openings deducted at half | 96 sq ftof 192 sq ft total |
| Net area | 1,389 sq ft |
| With 12% waste | 1,556 sq ft |
| Squares | 15.6 |
| Vinyl cartons at 2 squares | 8 |
| Starter strip | 140 ft |
| J channel | 196 ftaround windows and doors |
The material list this produces
| Siding, cartons at 2 squares | 8 |
|---|---|
| Starter strip, ft | 140 |
| J channel, ft | 196 |
| Outside corner posts, 10 ft | 4 |
| Undersill trim, ft | 140 |
| House wrap, sq ft | 1,485 |
| Siding nails, lb | 4 |
Roof pitch compared
Pitch only moves the gable triangles, but it moves them fast. Going from 4/12 to 12/12 triples the gable area on the same house, which is about three extra squares of siding on a 30 foot wide elevation and closer to six on a 40 foot one.
| Roof pitch | Siding needed | Gable area |
|---|---|---|
| 4/12 | 14.7 squares | 150 sq ft |
| 6/12 | 15.6 squares | 225 sq ft |
| 8/12 | 16.4 squares | 300 sq ft |
| 10/12 | 17.2 squares | 375 sq ft |
| 12/12 | 18.1 squares | 450 sq ft |
What else matters here
A 30 by 40 rectangle has a perimeter of 140 feet, which at nine feet of wall is 1,260 square feet before anything else. The two gables on the 30 foot ends add 225, and openings take 96 back off.
Fifteen point six squares, eight cartons. This is the cleanest possible siding job: four corners, one rectangle, two gables, no jogs.
Note which walls carry the gables. On a 30 by 40 with the ridge running the long way, the gables sit on the 30 foot ends, so the gable width is 30 and not 40. Gable width is always the width of the wall the triangle sits on, which is the short side on most houses.
What this calculator assumes
- A gable is a triangle, so its area is the width squared times the pitch divided by 48. Two gables on a 30 foot wide house at 6/12 add about 225 square feet, which is more than two squares of siding that people routinely forget.
- Openings are deducted at half, not in full. You still cut siding around a window and the offcut is usually scrap, so the trade rule is to take off half the opening and leave anything under 10 square feet in.
- 12 percent waste is normal for vinyl on a straightforward house. Lap siding, a cut up elevation or a staggered shake course runs higher.
- A carton of vinyl siding covers two squares, 200 square feet. Fiber cement and wood lap are sold by the piece, so use the square figure and convert at your supplier's coverage.
Questions people ask
How much siding for a 30x40 house?
About 15.6 squares, eight cartons of vinyl, with nine foot walls and two 6/12 gables on the 30 foot ends. The perimeter is 140 feet, which is the number the wall area comes from.
How do you calculate gable area?
Width squared times the pitch divided by 48. A 30 foot wide gable at 6/12 is 30 times 30 times 6 divided by 48, which is 112.5 square feet each, 225 for a pair. That shortcut is the triangle area formula with the rise already substituted out, so you never have to measure the height of the peak.
How many squares are in a box of vinyl siding?
Two. A standard carton covers 200 square feet, which is why siding is quoted in squares rather than square feet. Fiber cement and wood lap are sold by the piece, so take the square figure here and convert at whatever coverage your supplier lists.
The siding calculator takes any dimensions you like and hands back the same list.