Deck Calculator — Materials, Joists & Cost
Enter your deck dimensions to get board counts, joist and footing quantities, and a budget range. Sizing follows IRC R507 joist and post spacing practice.
Your numbers
Results
- Deck area
- 192 sq ft
- Estimated cost
- $6,854 – $9,274
- Decking rows5.5" board + 1/8" gap
- 26 rows
- Decking boards (16 ft)includes 8% waste
- 29 boards
- Joists @ 16" o.c.
- 13 pcs × 12 ft
- Beams / rim joists
- 3 runs × 16 ft
- Footings & postsguardrail required at 30" drop
- 6 footings
- Deck screws
- 2 boxes (350 ct)
Quantities are estimates for planning. Verify spans, spacing and local amendments before ordering.
How the math works
- Deck area = length × width. Board rows = deck width ÷ (board width + 1/8" gap), rounded up.
- Board count assumes 16 ft stock with 8% cut waste; order full lengths that span joists without butt joints where possible.
- Joist count = deck length ÷ spacing + 1. Footing count assumes posts every 8 ft along two beam lines.
Code & best practice
- IRC R507 sets joist and beam spans by species and spacing — 16" o.c. is the common default for 2x8 southern pine.
- Guardrails are required when the walking surface is more than 30" above grade (IRC R312).
- Ledger boards must be through-bolted or lagged to the rim joist, never nailed only (IRC R507.9).
Frequently asked questions
How many boards do I need for a 16x12 deck?
About 27 rows of 5.5" decking, or roughly 29 sixteen-foot boards including 8% waste.
How much does a deck cost per square foot?
Pressure-treated decks typically run $30–$45 per sq ft installed; composite decks run $50–$75 per sq ft depending on railing and framing height.
What joist spacing should I use?
16" on center is standard for most decking. Composite boards installed diagonally usually require 12" on center — check the manufacturer's instructions.