Deck Post Calculator
Calculate the number and size of posts needed for deck support based on deck dimensions and height.
Formula & Explanation
The deck post calculator determines how many posts are needed to support your deck. Formula: Posts per direction = floor(Length ÷ Spacing) + 1 Posts are arranged in a grid pattern. The total number of posts is: Total Posts = (Length Posts) × (Width Posts) Posts are typically spaced 8-12 feet apart for standard decks, depending on: - Deck height (taller decks need closer spacing) - Beam size and strength - Expected load (snow, occupancy) - Wood species and grade Post size is determined by height and load: - Up to 8 feet height: 4x4 posts typical - 8-12 feet height: 6x6 posts recommended - Over 12 feet: 6x6 or engineered solutions required
Assumptions
- •Posts are spaced equally in both directions
- •All posts support equal load (uniform grid)
- •Post size recommendations are preliminary; verify with local building code
- •Pressure-treated lumber grade #2 or better assumed
- •Posts sit on concrete footings below frost line
- •Post size does not account for unusual loads or extended cantilevers
Example Calculation
A 16x12 deck at 4 feet height with 8-foot post spacing needs 6 posts (3 along length × 2 along width) using 4x4 posts.
Inputs
Results
Post Size and Maximum Height by Spacing
| postSize | spacing4ft | spacing8ft | spacing12ft | maxHeight |
|---|---|---|---|---|
| 4x4 | 12+ ft | 8 ft | 6 ft | 8 ft |
| 6x6 | 16+ ft | 12 ft | 8 ft | 16+ ft |
| 4x6 | 14 ft | 10 ft | 7 ft | 12 ft |
| 6x8 | 18+ ft | 14 ft | 10 ft | 16+ ft |
| 8x8 | 20+ ft | 16 ft | 12 ft | 20+ ft |
| Double 2x6 | 12 ft | 8 ft | 6 ft | 8 ft |
Frequently Asked Questions
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