Deck Calculator
Enter your deck's dimensions and board spec to get boards, joists, and screws -- not just a raw square footage.
Deck boards needed
33 boards
Board rows
22
Joists
9
Deck screws
560
Deck area
160 sq ft
At the defaults above (a 16x10 ft deck, 5.5in boards, 16in OC joists) that's 33 boards, 9 joists, and 560 screws.
How it's calculated
Board rows come from the deck's width divided by each board's face width plus the gap between boards; each row runs the deck's full length, and the total linear footage (plus waste) is divided by your stock length and rounded up. Joists use the same "runs of spacing, plus one" counting logic as fence posts, spaced perpendicular to the boards. If your deck needs stairs down to grade, FrameSums' stair calculator sizes the rise, run, and stringers separately.
Keep going
- A deck and the fence enclosing the yard around it are often built together; the fence calculator uses the same post-spacing logic. Fence Calculator
- For an irregularly shaped deck, work out the real square footage here first, then bring that number into the board and joist counts. Square Footage Calculator
Frequently Asked Questions
Should my joists be 12in or 16in on-center?
16in on-center (OC) is the standard spacing most decking boards' span rating is built around; 12in OC is used for thicker or composite boards, or for longer spans, per most manufacturers' published span tables. Check your specific board's span rating before finalizing.
Why leave a gap between deck boards?
A small gap (commonly 1/8"-3/16") lets water drain through instead of pooling, and gives pressure-treated or composite boards room to expand and contract with temperature and moisture. This calculator defaults to 1/8".
Does composite decking need a different waste percentage than wood?
Composite is often cut more precisely and has less warping-related waste than natural wood, but 10% is a reasonable starting default for either -- adjust down slightly for composite if you have a very simple, rectangular deck shape.
How do board rows convert into a board count?
Each row runs the full length of the deck; multiply the row count by the deck length to get total linear feet needed, then divide by the stock length you're buying (8, 12, 16, or 20 ft) and round up -- that's what this calculator does automatically.
Does my deck need stairs?
If the deck sits above ground level, yes -- stair rise, run, and stringer sizing is a separate calculation from the deck surface itself. FrameSums' stair calculator handles that piece.