Hardie Siding Calculator

The part of each plank still visible after the one above overlaps it. It is always less than the plank's full width. A 7-inch exposure means each row shows 7 inches of face to the weather even though the board itself is wider, and that hidden strip is what keeps water out.

12 feet, which is why it is the default above. Some product lines and some regions carry other lengths, so check what your supplier actually stocks before ordering. Plank length feeds straight into the count, so a wrong assumption there throws the whole number off.

Narrower exposure means more overlap, which means less of each board is doing any covering, which means more boards for the same wall. Wider exposure covers faster and costs less, at the price of a bolder, less traditional reveal. It is an appearance decision with a budget attached.

Fiber cement lap siding comes as discrete planks at a fixed length, installed at an exposure you choose, so it gets counted by the piece. The general siding calculator works in squares of 100 sq ft, which suits panel and shake products better but tells you nothing about how many boards to put on the truck.