Deck Post Calculator
Estimate posts, post length, and concrete for your deck
Length along the supported beam
Total width of the deck
On-center spacing between posts
Post Length
—
ft
Concrete Bags
—
bags
Posts Needed
—
posts
Disclaimer: Results are estimates based on standard formulas. Not a substitute for professional advice from a licensed contractor, engineer, or architect. Verify all calculations before making purchasing or construction decisions.
How to Use This Calculator
Deck posts carry the entire load to the ground. Getting the count, height, and footing concrete right keeps your deck safe and code-compliant. Our calculator sizes posts for a typical beam-and-footing layout.
- Measure the deck length along the supported beam
- Enter the deck width for reference
- Set the on-center post spacing (typically 6-8 ft)
- Order 10% extra concrete to cover overpours and waste
Expert Insights
Smart analysis for your Decking project
Per-Side Post Count
Posts per long side equals ceil(deckLength / spacing) + 1. The calculator doubles that for both sides and adds 2 for the width spans.
Standard Post Length
A 4-foot post is the standard for low and ground-level decks, allowing for footing embedment plus deck height. Taller decks need longer posts.
Concrete Footing Rule
Each post footing uses roughly 3 bags of 60 lb concrete. Our AI multiplies post count by 3 for a quick total — round up when ordering.
Calculation Formula
Posts per Long Side = ceil(deckLength / postSpacing) + 1
Total Posts = (Posts per Long Side × 2) + 2
Post Length = 4 ft
Concrete Bags = Total Posts × 3
Deck Post Material Comparison
| Post Material | Size | Lifespan | Cost per Post | Best For |
|---|---|---|---|---|
| Pressure-Treated Pine | 4x4 / 6x6 | 20-30 yrs | $20-50 | Budget decks |
| Cedar | 4x4 / 6x6 | 20-25 yrs | $40-80 | Natural look |
| Redwood | 4x4 / 6x6 | 25-30 yrs | $60-120 | Premium decks |
| Steel (galvanized) | 3" / 4" | 50+ yrs | $80-150 | High-load decks |
Authority References
Our calculations are based on guidelines and standards from these authoritative sources:
- North American Deck & Railing Association (NADRA) — Deck Construction & Post Guidelines. Learn more
- International Residential Code (IRC) — Section R507 — Exterior Decks. Learn more
- American Concrete Institute (ACI) — Concrete Footing & Foundation Standards. Learn more
Frequently Asked Questions
How far apart should deck posts be?
Deck support posts are typically spaced 6 to 8 feet apart along the beam. This calculator uses your chosen post spacing and the deck length to count posts per long side.
How deep should deck post footings be?
Deck footings must extend below the frost line — typically 36 to 48 inches deep in cold US climates, and at least 12 inches in frost-free zones. Check your local IRC frost depth.
How many bags of concrete per deck post?
A standard deck post footing uses about 3 bags of 60 lb concrete. This calculator multiplies the post count by 3 to estimate total concrete bags.