Offline
No internet, no account required.
IRC R507
Validated against the standard.
PDF export
Pro-only. Generate professional reports.
$2.99 Pro
Lifetime unlock. No subscriptions.
How it works
Enter your values
Type in your inputs — the app fills code tables and constants for you, so there's nothing to look up.
Get a code-checked result
Instant answer with a clear PASS / FAIL and the exact IRC R507 reference behind every number.
Save & export
Keep a history of calculations and export a clean PDF report to share or attach to a permit (Pro).
What this calculator does
This app sizes deck framing and counts materials. It checks joist, beam, and post spans against the IRC R507 prescriptive tables and estimates the boards, joists, and fasteners you'll buy.
What it covers
- Joist span by lumber size, species, and spacing (12, 16, or 24 in on center).
- Beam size and post spacing from the tributary load (R507 beam tables).
- Footing size for the soil bearing capacity, and a material take-off for decking and hardware.
Worked example
2x8 southern pine joists at 16 in on center span roughly 12 to 13 ft under IRC R507; the app confirms the span and then counts the joists, decking boards, and hangers for your deck dimensions.
Related calculators
Verify joist spans with the span table reference and figure footings with the concrete calculator.
Deck FAQ
Which code does it use for spans?
The IRC R507 prescriptive deck tables for joists, beams, and posts, which most jurisdictions adopt for residential decks.
Does spacing change the span?
Yes. Tighter joist spacing (12 in vs 16 in vs 24 in on center) allows a longer span for the same lumber, which the app accounts for.
Does it estimate materials?
Yes — joist count, decking boards, and hardware, plus footing concrete you can pass to the concrete calculator.
Does it work offline?
Yes, it runs 100% offline with no account. Free with rewarded ads; a one-time $2.99 Pro unlock adds PDF export and saved history.
Get Deck Calculator on your phone
Free with rewarded ads · $2.99 lifetime Pro · iOS & Android. Works 100% offline on the job site.