Part of the DIY & Home collection — 4 tools available
Deck Calculator — Boards & Framing
Calculate deck boards, joists, posts, and total lumber needed for your deck project. Get a complete material list and cost estimate for deck construction.
About This Calculator
Building a deck is a major DIY project, and ordering the wrong amount of lumber means either halting work mid-build or returning heavy boards to the lumber yard. Deck construction requires multiple material types: decking boards, joists, beams, posts, concrete footings, railings, and hardware — each calculated differently based on your deck dimensions and joist spacing. A 12*16 foot deck with 16-inch joist spacing needs 13 joists, 26 decking boards, and 6 concrete footings at minimum. Our deck calculator breaks down every component for a complete and accurate material list.
The Formula Behind This Calculator
Area = Length * Width Joists = Floor(Width / Spacing) + 1 Boards = Area / Board width
Understanding the math helps you verify results and make better decisions for your project.
How to Use
- 1Enter deck length and width in feet.
- 2Set deck board width (5.5" for standard 2*6, 3.5" for 2*4).
- 3Set gap between boards (1/8" for composite, up to 1/4" for wood).
- 4Set joist spacing (16" standard, 12" for composite decking).
- 5Enter price per linear foot of decking board.
- 6Click Calculate for board count, joists, and cost.
When to Use
- →Building a deck and needing a complete lumber shopping list before the first trip to the yard
- →Comparing material costs between wood, composite, and PVC decking for the same deck size
- →Estimating DIY deck costs vs getting a contractor quote to see if the labor savings are worth it
Tips
- ✓Use 12-inch joist spacing for composite decking — 16-inch spacing may void the manufacturer warranty
- ✓Pressure-treated lumber shrinks as it dries — gap boards 1/8 inch when installing wet wood to allow for expansion
- ✓Budget for hidden fasteners, joist hangers, post anchors, and concrete — they add 20-30% to the lumber cost
FAQ
Should I use 2×6 or 5/4 decking boards?
2×6 (actual 1.5×5.5") is stronger and better for spans over 16". 5/4 (actual 1×5.5") is fine for 16" joist spacing and has a slightly rounded profile many find more comfortable underfoot.
How far apart should deck joists be?
Wood decking: 16" on center. Composite decking: 12-16" depending on the manufacturer (check specs). Diagonal decking requires 12" spacing.
What is the average cost to build a deck?
Pressure-treated wood: $15-25/sq ft installed. Composite: $30-45/sq ft. PVC and hardwood: $35-60/sq ft. DIY saves roughly 50% vs hiring a contractor.
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