21 calculators · IRC 2021 · Free forever
Pass code inspection
Every structural calculator validates against IRC 2021: joist span (R507.6), beam span (R507.5), footings (R507.3), guards (R312), and stairs (R311.7). Results display compliance badges with the exact code section used, so you have a paper trail for the building inspector.
Are DeckMath calculators IRC 2021 compliant?
Yes. Every structural calculator validates against IRC 2021 — joist span (R507.6), beam span (R507.5), footings (R507.3), guards (R312), and stairs (R311.7). Results display compliance badges with the exact code section used, giving you a paper trail for the building inspector.
21 calculators
Will my deck pass IRC inspection?
Joist Span Calculator
Maximum joist span for any size, species, and spacing — directly from IRC 2021 R507.6 tables.
Deck Beam Span Calculator
Maximum beam span (post-to-post) by size, ply, species, and tributary load — straight from IRC R507.5 / DCA-6.
Deck Footing Calculator
Footing diameter, depth, concrete volume, and bag count — IRC R507.3 sized + frost depth lookup for all 50 states.
Footing Depth Calculator
Per-footing IRC R507.3 sizer: depth from frost + structural, diameter from soil bearing, rebar spec, concrete order. 5 soils × 4 footing types.
Footing Diameter Calculator
Footing diameter sizing — sonotube + Bigfoot Ø by post tributary load + soil bearing capacity. IRC R403.1.4 + R507.3.1 compliance. 8″-24″ Ø range × 5 soil tiers.
Frost Depth Calculator
IRC R403.1.4 footing-depth lookup. State + 80+ metro lookup, soil + elevation refinement, FPSF strategy. Free + free forever.
Baluster Spacing Calculator
Even baluster spacing for any railing length — IRC R312.1.3 4-inch sphere check, 7 styles, 1/16″ precision, side-elevation SVG.
Stair Handrail Calculator
IRC R311.7.8 stair-handrail design. Type 1/Type 2 grip validation, 34-38" height check, returns + ADA 505 mode. 7 materials × 4 mounting styles. Full hardware BoM with brackets + return fittings.
Stair Riser Calculator
Riser count + LF + cost for any stair style (closed/open/skirt). IRC R311.7.5.1 max 7.75″ + open-riser ≤ 4″ sphere check. 4 materials.
Stair Rise and Run Calculator
Equal-rise riser distribution, run depth, stringer hypotenuse, and angle for any deck height. IRC R311.7.5 + Blondel 2R + T ergonomic check. Permit-ready callout sheet.
Stair Stringer Calculator
Stringer hypotenuse, notch depth, throat (DCA-6 ≥ 5″), stringer count, stock-length pick, brackets + fasteners. IRC R311.7 + AWC DCA-6 cross-validated.
Deck Cantilever Calculator
IRC R507.6 joist overhang validator. Checks 3 rules: L/4 of back-span, 24″ absolute, total joist span. Pass/fail + beam moment multiplier + blocking spec. AWC DCA-6 backed.
Deck Joist Blocking Calculator
Joist blocking count + LF + cost. IRC R502.7.1 mid-span (required for joists > 8 ft) + perimeter rows. Match floor joist depth (2×8/2×10/2×12).
Deck Ledger Board Calculator
Size your deck ledger board: joist span × load × snow × ledger length → 2×8/2×10/2×12 PT or LVL recommendation. IRC R507.9 compliant. Flashing strategy.
Ledger Bolt Calculator
Ledger bolt count + spacing per IRC R507.9.1.3. Lag screw / through-bolt / SDS structural screw options vs deck tributary load. Edge + end distance + spacing compliance.
Lateral Load Calculator
IRC R507.9.2 lateral connection design. Simpson DTT2Z hold-down count + spacing. Earthquake + wind lateral capacity check. Inspection-grade output.
Deck Post Size Calculator
Size deck posts given tributary load + post height. 4×4 / 6×6 / 8×8 / steel recommendation per IRC R507.4. Column-buckling-aware + footing match.
Deck Post Spacing Calculator
IRC R507.5 beam-to-post spacing sizer. 12 beam profiles (double/triple 2×8/10/12, solid 4×6 to 6×10), 4 species, tributary + load. Post count + post size + Simpson connector spec. DCA-6 backed.
Snow Load Calculator
ASCE 7-22 design snow PSF for deck framing. 50 state defaults per IRC R301.2(5), elevation adjustment, exposure factor, drift load math. Upstream input for Joist + Beam + Deck Load + Ledger Bolt.
Soil Bearing Calculator
Soil identification helper — 8 soil types with presumptive PSF per IRC R401.4.1, wet-condition load reductions, when to require a soil test. Drives footing diameter math.
Deck Load Calculator
Reverse-check 'how much weight can my deck hold?' — joist + beam + post + footing vs live + dead + snow + point loads per IRC R301.5 + R507. Hot tub + outdoor kitchen + planter presets.
Other paths
All 121 calculators →Frequently asked
About this path
- Which IRC sections do DeckMath calculators cover?
- Joist span (R507.6), beam span (R507.5), footings (R507.3 and R403), ledger attachment (R507.9), lateral load (R507.9.2), stairs (R311.7), guards/balusters (R312), and handrails (R311.7.8) all reference the published IRC 2021 tables.
- Will inspectors accept DeckMath as proof of compliance?
- DeckMath shows the IRC table values used in each calculation. Inspectors verify the inputs (joist size, species, spacing) and confirm the result against the same tables — most accept printed results as part of the permit package, but always check with your local building department.
- What if my deck doesn't fit the IRC prescriptive path?
- DeckMath flags decks that exceed prescriptive limits (cantilevers over 24 inches, multi-level connections, hot tubs, or commercial loads). These require an engineer's stamp — the calculator surfaces the trigger so you know early.
- Do calculators check guardrail height and baluster spacing?
- Yes. The Baluster Spacing Calculator enforces the 4-inch sphere rule (IRC R312.1.3) and the Handrail Calculator validates the 36-inch minimum guard height (R312.1.2) plus 34–38 inch handrail height (R311.7.8.1).