Siding Calculator: Squares, Cartons and Trim
Perimeter, wall height, the gables and the openings, and it returns the net area, the squares, the cartons and the trim. The gables are the part people leave out, and on an ordinary house they are worth more than two squares on their own.
When the figures look right, the siding material list downloads as a real PDF with your business details on it, built inside your own browser. Nothing you type is uploaded anywhere.
Worked example
These are the figures the calculator opens with and the answer it gives. Change anything above and every number below moves with it.
- Wall perimeter150 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 needed16.6 squares
| Wall area | 1,350 sq ft |
|---|---|
| Gable area | 225 sq ft2 gables at 6/12 |
| Openings deducted at half | 96 sq ftof 192 sq ft total |
| Net area | 1,479 sq ft |
| With 12% waste | 1,656 sq ft |
| Squares | 16.6 |
| Vinyl cartons at 2 squares | 9 |
| Starter strip | 150 ft |
| J channel | 196 ftaround windows and doors |
The material list this produces
| Siding, cartons at 2 squares | 9 |
|---|---|
| Starter strip, ft | 150 |
| J channel, ft | 196 |
| Outside corner posts, 10 ft | 4 |
| Undersill trim, ft | 150 |
| House wrap, sq ft | 1,575 |
| Siding nails, lb | 5 |
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.
Gables are a triangle and they are always forgotten
The area of a gable is its width squared, times the pitch, divided by 48. It falls straight out of the triangle: the height is half the width times the rise over twelve, and the area is half the base times the height.
Two gables on a 30 foot wide house at 6/12 come to 225 square feet. That is two and a quarter squares, more than one carton of vinyl, and it is the single most common reason a siding order comes up short.
Steeper roofs make it worse fast, because the figure scales with the pitch. The same house at 12/12 has 450 square feet of gable, which is four and a half squares.
Deduct half an opening, not all of it
A window is a hole in the wall, so the instinct is to subtract its full area. The siding says otherwise. Every course that meets a window gets cut around it and the offcut is usually scrap, so some of the material you removed from the take off gets consumed anyway.
The trade rule is to deduct half the opening area, and to ignore anything under about ten square feet entirely. This calculator uses windows at 15 square feet and doors at 21, then takes half, which is the standard approach and lands close on an ordinary house.
If the elevation is mostly glass, measure the openings properly rather than counting them, because at that point the halving rule is doing too much work.
The trim is where the order goes wrong
Siding is sold in cartons of two squares and that part is easy. The accessories are the part that gets missed: starter strip around the whole base, J channel around every window and door, outside corner posts in ten foot lengths, undersill trim under every window and at the top course.
J channel here is figured at 16 feet a window and 18 a door, which covers the head and two jambs with the usual overlap. Corner posts come from the corner count times the wall height, in ten foot sticks.
House wrap is figured on the gross wall area, openings included, because it goes on before the windows are cut in and you do not want to be piecing it.
Questions people ask
How many squares of siding do I need?
Take the wall perimeter times the height, add the gables, subtract half the opening area, then add waste. A 150 foot perimeter with 9 foot walls, two 30 foot gables at 6/12, ten windows and two doors comes to 16.6 squares at 12 percent waste. Put your own numbers in above.
How do I calculate gable area for siding?
Width squared, times the roof pitch, divided by 48. A 30 foot wide gable at 6/12 is 900 times 6 divided by 48, which is 112.5 square feet per gable.
How much siding is in a carton?
This calculator counts a vinyl carton as two squares, 200 square feet. For siding sold by the piece, use the square figure here and convert at your supplier's number.
Free Contractor Estimate Template, free, no signup, PDF Word and Excel.
Common sizes, worked out
The same calculator with the numbers already filled in, one page per size, each ending in its own material list.
More sizes, answered
Each row is this calculator run with those numbers when the page was built. Type the same numbers in above to see every line of the working.
| Example | What it assumes | Siding needed |
|---|---|---|
| 2,000 sq ft house | 180 ft perimeter, 9 ft walls, two 34 ft gables at 6/12, 14 windows, 2 doors, 12% waste. | 20 squares |
| 2,500 sq ft house | 200 ft perimeter, 9 ft walls, two 38 ft gables at 6/12, 16 windows, 3 doors, 6 corners, 12% waste. | 22.5 squares |
| 30 x 40 house | 140 ft perimeter, 9 ft walls, two 30 ft gables at 6/12, 10 windows, 2 doors, 12% waste. | 15.6 squares |
| Ranch, 1,200 sq ft | 150 ft perimeter, 9 ft walls, two 26 ft gables at 4/12, 10 windows, 2 doors, 12% waste. | 15.3 squares |
| 1,800 sq ft house | 170 ft perimeter, 9 ft walls, two 32 ft gables at 6/12, 13 windows, 2 doors, 12% waste. | 18.7 squares |