deck beam span calculator · 720/mo searches
Deck Beam Span Calculator (IRC R507.5)
A deck beam's allowable span between posts depends on the beam size and the joist span it supports. Enter your deck and the calculator pulls the maximum post spacing from IRC Table R507.5 and tells you how many posts you need.
Member sizes read from the IRC R507.6 (joists) and R507.5 (beams) tables for No. 2 Southern Pineat 40 psf live + 10 psf dead. Footings from tributary load ÷ soil bearing (R507.3); ledger fasteners per R507.9. Confirm with your local building department.
| Decking: Pressure-treated pine192 sq ft · ~28 × 16′ boards · Shop materials ↗ | $575–$1,730 |
| Substructure (joists, beam, posts, hardware)192 sq ft framing · Shop materials ↗ | $1,150–$2,495 |
| Footings (concrete piers)4 posts · Shop materials ↗ | $140–$360 |
| Railing / guard40 lin ft · Shop materials ↗ | $600–$2,400 |
| Stairs4 treads · Shop materials ↗ | $120–$380 |
| Permit + fasteners + miscallowance | $75–$500 |
| Total estimate | $2,660–$7,865 |
Low is a DIY material budget; high is contractor-installed with labor. Regional prices vary, so treat this as a planning range, not a quote.
Prefer to hire it out? Get free quotes from local deck builders →
Turn this deck into a permit-ready PDF: title block, elevation, framing & footing schedules, code citations.
Full deck beam span table (IRC R507.5)
| Beam | 6′ | 8′ | 10′ | 12′ | 14′ | 16′ | 18′ |
|---|---|---|---|---|---|---|---|
| 2×2x6 | 6'11" | 5'11" | 5'4" | 4'10" | 4'6" | 4'3" | 4' |
| 2×2x8 | 8'9" | 7'7" | 6'9" | 6'2" | 5'9" | 5'4" | 5' |
| 2×2x10 | 10'4" | 9' | 8' | 7'4" | 6'9" | 6'4" | 6' |
| 2×2x12 | 12'2" | 10'7" | 9'5" | 8'7" | 8' | 7'6" | 7' |
| 3×2x8 | 10'10" | 9'6" | 8'6" | 7'9" | 7'2" | 6'8" | 6'4" |
| 3×2x10 | 13' | 11'3" | 10' | 9'2" | 8'6" | 7'11" | 7'6" |
| 3×2x12 | 15'3" | 13'3" | 11'10" | 10'9" | 10' | 9'4" | 8'10" |
| Beam | 6′ | 8′ | 10′ | 12′ | 14′ | 16′ | 18′ |
|---|---|---|---|---|---|---|---|
| 2×2x6 | 5'5" | 4'8" | 4'2" | 3'10" | 3'6" | 3'1" | 2'9" |
| 2×2x8 | 6'10" | 5'11" | 5'4" | 4'10" | 4'6" | 4'1" | 3'8" |
| 2×2x10 | 8'4" | 7'3" | 6'6" | 5'11" | 5'6" | 5'1" | 4'8" |
| 2×2x12 | 9'8" | 8'5" | 7'6" | 6'10" | 6'4" | 5'11" | 5'7" |
| 3×2x8 | 9'8" | 8'6" | 7'7" | 6'11" | 6'5" | 6' | 5'8" |
| 3×2x10 | 12' | 10'5" | 9'4" | 8'6" | 7'10" | 7'4" | 6'11" |
| 3×2x12 | 13'11" | 12'1" | 10'9" | 9'10" | 9'1" | 8'6" | 8'1" |
Deck Beam Span: what to know
- •Beam span is driven by the supported joist span: the longer the joists, the more load on the beam, the shorter it can span.
- •A 3-ply beam spans noticeably further than a 2-ply of the same depth, often the cheapest way to drop a post.
- •Built-up beams must be fastened per IRC R507.5.2; a dropped beam needs post-to-beam connectors rated for uplift.
Want a permit-ready deck plan?
This estimate is built for planning. For your permit packet, DeckHelm Pro turns these numbers into a code-referenced framing plan, footing schedule and material list as a printable PDF.
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