Decking Calculator

Divide the deck width (in inches) by the effective board width (board width plus gap) to get the number of rows, then multiply by the number of board lengths needed to span the deck length. Add a waste factor of at least 10% for cuts and defects.

For pressure-treated lumber, 1/8 inch (about the width of a 16d nail) is standard — the wood shrinks as it dries, so a tight fit can leave a small natural gap. For pre-dried or composite boards that won't shrink, use a 3/16 inch spacer to ensure drainage and airflow.

A 10% waste allowance is typical for a straightforward rectangular deck. Add 15–20% for diagonal patterns, picture-frame borders, or heavily knotted lumber. It is better to order extra than to run short and risk a color mismatch on a second order.