Siding Calculator
Siding Calculator
Work out how much siding a house needs from its length, width and wall height, with the gable ends added and windows, doors and garage doors taken off. The page gives squares, boxes of vinyl or fiber cement planks, the trim that goes with them, and the cost.
The walls you are covering
How the area adds up
Wall area is the perimeter times the height to the eaves; each gable end adds a triangle half as wide as the house times the rise, which comes from the roof pitch. Windows are taken off at 3 x 4 ft, doors at 3 x 7 ft and garage doors at 16 x 7 ft. A square of siding is 100 sq ft, and a box of vinyl usually holds two squares. Fiber cement lap planks are 12 ft long and lap 1 1/4 in, so an 8 1/4 in plank shows 7 in and covers 7 sq ft, which matches the maker’s pieces per square for every width except 12 in, where this page rounds up to 10. Trim assumes four outside corners, starter strip around the base and J channel around every opening, in 12 ft 6 in pieces with 10 ft corner posts. The CSV, image and printed report contain the values you entered, nothing preloaded.
How to use this tool
Enter the house’s outside length and width and the wall height from the bottom of the siding to the eaves. Set the number of gable ends and the roof pitch, and the number of windows, doors and garage doors. Choose vinyl or fiber cement lap siding, and the page gives the squares to order, the boxes or planks, and the trim.
The drawing shows one long wall and one end wall to scale with the gable; the chart builds the order from walls and gables, less openings, plus waste. The table lists the starter strip, J channel and corner posts for the house.
How the siding is worked out
The walls are the perimeter times the height. Each gable end is a triangle as wide as the house, rising half the width times the pitch over 12. Openings come off at standard sizes, and the waste allowance, 10 percent by default, covers cuts, overlaps and mistakes. A square is 100 sq ft, so the order in square feet divided by 100 is the squares.
Vinyl siding comes in boxes of two squares. Fiber cement lap siding comes in 12 ft planks that overlap by 1 1/4 in, so each plank covers 12 ft times its exposed height: 7 sq ft for an 8 1/4 in plank, which is 15 planks to the square.
Siding for common house sizes
| House | Net wall area | Squares with 10% | Vinyl boxes | 8 1/4 in planks |
|---|---|---|---|---|
| 24 x 32 ft | 990 sq ft | 10.89 | 6 | 156 |
| 28 x 40 ft | 1,258 sq ft | 13.84 | 7 | 198 |
| 30 x 40 ft | 1,323 sq ft | 14.55 | 8 | 208 |
| 30 x 50 ft | 1,503 sq ft | 16.53 | 9 | 237 |
| 36 x 48 ft | 1,674 sq ft | 18.41 | 10 | 264 |
| 40 x 60 ft | 2,038 sq ft | 22.42 | 12 | 321 |
Single story, 9 ft walls, two gable ends at 6/12, 10 windows and 2 doors taken off, 10 percent waste.
A worked example you can check on paper
A single story house is 30 by 40 ft with 9 ft walls. The perimeter is 140 ft, so the walls are 1,260 sq ft. The two 30 ft gable ends at 6/12 each rise 7.5 ft, making triangles of 112.5 sq ft, 225 in all. Ten 3 x 4 ft windows and two 3 x 7 ft doors take off 162 sq ft, leaving 1,323 sq ft.
With 10 percent for waste that is 1,455 sq ft, 14.55 squares. In vinyl, at two squares a box, order 8 boxes. In 8 1/4 in fiber cement, each plank covers 7 sq ft, so 1,455 divided by 7 is 208 planks. The trim is about 140 ft of starter strip, 174 ft of J channel round the openings and four corner posts.
Vinyl or fiber cement
Vinyl is the cheapest to buy and install, needs no paint and is light enough for one person to handle, but it can crack in hard frost and dent or melt near a grill. Fiber cement looks more like painted wood, resists fire and insects and lasts well, but it is heavy, needs cutting with dust control, has to be painted and costs more to install. Both are ordered by the square.
Mistakes that catch people out
Using the floor area. Siding covers walls; a two story house has twice the wall of a bungalow with the same floor area.
Forgetting the gables. They can add a fifth to the wall area on a narrow house with a steep roof.
Measuring to the roofline. Measure the walls to the eaves; the soffit and fascia are separate trim.
Skipping the trim. Starter strip, J channel and corner posts are sold separately and add up.
Ordering exactly. Siding is cut and overlapped; order the waste allowance and match color batches.
Popular calculations
Each opens the calculator with its own address, and every value can be changed once it is open.
Single story houses, vinyl
Two story houses
Fiber cement
Garages and sheds
Metric
How this was checked
The engine was tested in Node against hand calculations: a 30 by 40 ft house with 9 ft walls, two 6/12 gables, ten windows and two doors gives exactly 1,260 sq ft of wall, 225 sq ft of gable, 1,323 sq ft net and 14.553 squares with 10 percent waste. Fiber cement pieces per square were checked against the maker’s chart, 25, 20, 17, 15 and 13 for 5 1/4 to 9 1/4 in planks, and openings larger than the walls are caught with a message.
Every address in the lists above was then opened and checked for a distinct title, the right answer, drawings that render, and clean CSV, image and print output containing only that calculation, at desktop, tablet and phone widths.
Common questions
What is a square of siding?
A square is 100 sq ft of wall covered. Siding, like roofing, is priced and ordered by the square, so 1,455 sq ft is 14.55 squares.
How much does a box of vinyl siding cover?
Usually two squares, 200 sq ft. Panel length and profile vary, so check the coverage printed on the box before ordering.
How do I calculate siding for a gable end?
A gable is a triangle: half the width of the house times the rise. The rise is half the width times the pitch over 12, so a 30 ft wide end at 6/12 rises 7.5 ft and the gable is 30 times 7.5 divided by 2, 112.5 sq ft.
How many squares of siding does a 2,000 sq ft house need?
It depends on the walls, not the floor. A single story 40 by 50 ft house with 9 ft walls and two 6/12 gables has about 1,858 sq ft of wall after windows and doors, which is about 20.4 squares with 10 percent waste. A two story house with the same floor area has far more wall.
How many pieces of fiber cement lap siding are in a square?
For 12 ft planks, 25 pieces of 5 1/4 in, 20 of 6 1/4 in, 17 of 7 1/4 in, 15 of 8 1/4 in and 13 of 9 1/4 in, because each plank shows its width less a 1 1/4 in lap.
Should I subtract windows and doors from siding?
Take off large openings such as garage and patio doors. Many installers leave small windows in, since the cutting around them uses much of the material saved, and treat the difference as part of the waste allowance.
Related Calculators and Reference
- Roof Squares Calculator: roofing squares for the same house.
- Plywood Calculator: wall sheathing under the siding.
- Paint Coverage Calculator: paint for fiber cement or wood siding.
- Square Footage Calculator: for walls with bump outs and odd shapes.
- Brick Calculator: if part of the house is brick instead.
- James Hardie: lap siding product details: plank sizes, exposures and installation.