Planks come in several widths; pick yours from the list or type the exposure from the manufacturer's installation guide.
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 many fiber cement planks per square?
With 8¼-inch planks at a 7-inch exposure, 100 ÷ 7 = about 14.3 planks per square, so 15 to be safe.
What exposure for 8¼ inch lap siding?
7 inches is the usual exposure, giving 1¼ inches of overlap. Check your product's installation instructions.
Does this work for wood lap siding?
Yes. Enter the board length and the exposure you plan to use.
Is SidingCalc free?
Yes, with no sign-up or ads.
Are my measurements saved?
Yes, in this browser only.