For an L-shaped or more complex house, measure each wall as a rectangle and add them, or run the calculator once per section.
How the siding calculator works
SidingCalc adds the four walls, 2 × (length + width) × wall height, and the gable triangles, ½ × width × gable height, where the gable height is half the width × pitch ÷ 12. It subtracts each window, door and garage door (count × width × height), adds the waste allowance and divides by 100 for squares. Lap planks = order area ÷ (plank length × exposure). Trim is rounded up to whole pieces.
Lap plank coverage (12 ft planks)
| Plank | Exposure | Sq ft per plank | Planks per square |
|---|---|---|---|
| 5¼″ fiber cement plank | 4″ | 4 | 25 |
| 6¼″ fiber cement plank | 5″ | 5 | 20 |
| 7¼″ fiber cement plank | 6″ | 6 | 16.7 |
| 8¼″ fiber cement plank | 7″ | 7 | 14.3 |
| 9¼″ fiber cement plank | 8″ | 8 | 12.5 |
Gable height by roof pitch (24 ft wide house)
| Pitch | Gable height | Area per gable |
|---|---|---|
| 4/12 | 4 ft | 48 sq ft |
| 6/12 | 6 ft | 72 sq ft |
| 8/12 | 8 ft | 96 sq ft |
| 10/12 | 10 ft | 120 sq ft |
| 12/12 | 12 ft | 144 sq ft |
Exposures are typical for fiber cement lap siding; follow the manufacturer's installation guide for your product. Box coverage and trim lengths vary by brand. Results are estimates: check them against your own wall measurements and your supplier's take-off before you order.
Frequently asked questions
How much siding do I need for a 40 × 30 house?
With 9 ft walls, two 6/12 gables, 10 windows, 2 doors and a garage door: 1,181 sq ft net, about 13 squares with 10% waste, or 7 boxes of 2 squares.
What is a square of siding?
100 square feet of wall coverage. Vinyl siding is priced and boxed by the square, often 2 squares per box.
Should I subtract windows and doors?
Yes for an accurate count, but many installers skip small windows and keep the waste allowance at 10% or more for cuts around them.
Is SidingCalc free?
Yes, with no sign-up or ads.
Are my measurements saved?
Yes, in this browser only.