IRC R507 · AWC DCA6 · 50 states
Size your deck to code,
in under a minute.
The free calculator that reads the real IRC span tablesto size your joists, beams, posts, footings and stairs — with your state's frost depth and a permit-ready framing plan. No guessing, no fees.
- 7
- calculators
- 50
- states covered
- $0
- to run the math
The calculator
Enter your deck. Get a code-compliant plan.
Change any input and the framing plan, span checks, cost and materials update live. Everything below is free and needs no account.
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.
Why it's different
A spec, not a guess
Most “deck calculators” hand you a rounded rule of thumb. DeckHelm returns the actual member sizes the building code prescribes, with the citation attached.
The real code tables
Not estimates. Every joist and beam size is read straight from IRC Tables R507.6 and R507.5 for No. 2 lumber — the same tables your plans examiner uses.
Your state’s frost depth
Footing depth is set to the frost line where you build, from 12″ in the frost-free South to 60″ up north — all 50 states.
Permit-ready output
A scaled framing plan, footing schedule, ledger fastening and stair layout, each with its code citation for your submittal.
Free, in seconds
No account, no paywall on the math. Size an entire deck — joists to stairs — in under a minute, then print it.
How it works
From backyard sketch to permit packet
- 01
Enter your deck
Width, projection, height, lumber species and your state. Two numbers and two dropdowns.
- 02
We read the code
The engine pulls joist and beam spans, footing size and depth, ledger spacing and stair layout from the IRC in real time.
- 03
Build or submit
Print the framing plan, shop the itemised material list, or hand the numbers to a local builder for a quote.
Built on the actual code
Every number traces back to a table
DeckHelm doesn't invent spans. The engine transcribes the prescriptive tables that residential decks are built to, so the plan you print matches what your inspector checks line for line.
Every part of the deck
Pick the calculator you need
Why it matters
Why build to the deck code?
Deck collapses are almost always a framing or connection failure: an undersized beam, joists spanning too far, a ledger lag-bolted into nothing, or footings that heaved out of the ground over one winter. That's why the building code (the IRC, Section R507) sets prescriptive span tables for exactly this: residential wood decks built without an engineer.
The trouble is the tables are dense. Joist spans change with size, spacing and species; beam spans depend on the joist span they carry; footing depth tracks the frost line where you live. This calculator reads those tables for you and returns a complete framing plan, each figure with its code reference so your drawings match what the inspector checks.
FAQ
Common questions
- How do I size deck joists, beams and footings?
- Pick the joist span from IRC Table R507.6 (by joist size, spacing and lumber species), the beam from Table R507.5 (by the joist span it carries), and the footing from the post's tributary load divided by your soil's bearing value. The calculator above does all three at once and shows the code reference for each.
- How far can a 2x8 deck joist span?
- A No. 2 Southern Pine 2x8 spans up to 13'1" at 12" on-center, 11'10" at 16", and 9'8" at 24", per IRC R507.6. Douglas Fir-Larch and Hem-Fir span a little less, and cedar/redwood less again. The tool picks the smallest joist that clears your projection automatically.
- How deep do deck footings need to be?
- Footings must bear below the local frost line so they can't heave. That ranges from about 12" in frost-free states to 60" in the upper Midwest and New England. Choose your state in the calculator and it sets the depth; always confirm the exact figure with your building department.
- Do I need a permit to build a deck?
- Almost everywhere, yes. Most jurisdictions require a permit for any deck attached to the house or more than ~30" above grade, plus an inspection of the footings before they're poured. The calculator's framing plan is built to the IRC so your drawings line up with what the inspector checks.
Deck building guides
Code-grounded, plain-English answers
Your deck, sized and specced — free.
Run the numbers now, or turn them into a permit-ready PDF with DeckHelm Pro. Prefer to hire it out? We'll pass your project to deck builders in your area.
- Joist & beam sizing to IRC R507
- Footing depth for all 50 states
- Stair & guard layout to R311/R312
- Itemised material list & cost range