Decking Calculator
Free decking calculator—estimate boards from deck area, board width, gap, and board length.
Results
27Boards to buy
- 198Board face coverage (sq ft)
How it works
Spacing = board width + gap. Boards = ceil(deck area ÷ ((spacing÷12) × board length)).
Worked example
Example: 200 sq ft deck, 5.5 in boards, 0.125 in gap, 16 ft lengths → 27 boards.
Nominal vs actual width
A “6 inch” board is often about 5.5 inches actual. Enter the actual face width you will install.
Gaps
Wood and many composites need a side gap for drainage and expansion—often about 1/8 in. Enter the gap your fastener system specifies.
Hidden fasteners
Board count is unchanged by fastener type. Order fascia and picture-frame boards separately.
Frequently asked questions
How many deck boards do I need?
Divide deck square footage by the footprint of one board including its side gap, then round up.
What about stairs and railing?
This tool sizes the deck surface only. Stair treads and rail parts are separate takeoffs.
Composite vs wood?
Use the board size and gap for the product you buy. Coverage math is the same; spanning rules differ by brand.
Estimates only. Verify coverage rates and local requirements before purchasing materials. Not a substitute for professional advice.