Deck Calculator

Decking board count starts with how much of the deck's width each board actually covers: its real width plus the gap left for drainage and expansion, typically 1/8 in. Divide the deck's width by that number to get how many rows of boards run the length of the deck, then figure how many 8 ft boards each row needs based on the deck's length.

Joist spacing follows the decking manufacturer's span table — composite decking commonly requires 16 in on-center joists, while some products allow 12 in for diagonal installs. Count joists by dividing the deck's width by the spacing and adding one for the starting joist.

Stain and sealer coverage works like paint: total square footage times the number of coats, divided by the product's coverage rate per gallon, which is usually lower on rough-sawn decking than on smooth siding.

Where these numbers come from

These are planning estimates. Check product labels, your local building code, and a licensed contractor before you buy materials or build.