Siding calculator
Enter the house's walls and gables. You get the area net of openings, squares to order with waste, and the number of lap planks for the width and length you pick.
Inputs
Result
How it is worked out
A 40 by 28 ft house with 9 ft walls has 1,224 sq ft of wall. Two 6/12 gables 28 ft wide add 98 sq ft each. Less 200 sq ft of openings that is 1,220 sq ft, or 13.4 squares with 10% waste. 8-1/4 in planks lapped 1-1/4 in show 7 in each, so a 12 ft plank covers 7 sq ft: 192 planks.
Exposure
Lap siding covers less than its width because each course overlaps the one below. James Hardie calls for at least 1-1/4 in of lap on HardiePlank, which is why an 8-1/4 in plank shows 7 in and a 6-1/4 in plank shows 5. Vinyl is sold by the square, usually two squares to a box, with the exposure built into the panel.
Trim, corners, J-channel, starter strip and soffit are separate items and are measured in linear feet around every corner, opening and eave.
Questions
How many squares of siding do I need?
Add the wall area and the gable triangles, subtract doors and windows, add 10% and divide by 100. A 40 x 28 ft house with 9 ft walls and two 6/12 gables needs about 13.4 squares.
How many Hardie planks are in a square?
About 14.3 of the 8-1/4 in x 12 ft plank at a 7 in exposure, since each covers 7 sq ft. 6-1/4 in planks cover 5 sq ft each, so 20 to the square.
How do I calculate the area of a gable?
Half the width times the gable's height. The height is half the width times the pitch divided by 12, so a 28 ft wide gable at 6/12 is 14 x 7 = 98 sq ft.
Should I subtract windows from siding?
Yes, but subtract them before adding waste, and leave small windows in if you prefer; the offcuts around them are mostly waste anyway.
What is the exposure on Hardie siding?
The plank width less at least 1-1/4 in of lap: 4 in for 5-1/4 in planks, 5 for 6-1/4, 6 for 7-1/4, 7 for 8-1/4 and 8 for 9-1/4.
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