Deck Board Calculator

Calculate how many deck boards, joists, and posts you need to build a deck. Works for wood and composite decking.

Results are estimates only — actual material needs vary by site conditions, waste, and product specifications. Always verify quantities with a qualified contractor before purchasing. HandymanCalc is not liable for material shortfalls or overages.

Deck Size
ft
ft
Decking
FAQ

Frequently Asked Questions

3 questions
Q1 How far apart should deck joists be?
Space deck joists 16 inches on center for 5/4 decking. For composite decking, check the manufacturer specs — many require 12" on center.
Q2 How many deck boards do I need for a 12×16 deck?
A 12×16 deck (192 sq ft) using standard 5/4×6 boards (5.5" wide) needs approximately 42 boards at 16 feet long. Add 10% for waste.
Q3 What is the gap between deck boards?
Leave 1/8 inch gap between deck boards when installing dry lumber — it will expand when wet. Composite manufacturers specify their own requirements.