DeckMath

7 calculators · IRC 2021 · Free forever

Plan a new deck

Seven calculators in the order a deck actually gets built — start with dimensions, verify structural sizing, lay out footings, design stairs and railings, then estimate total cost. Each step feeds the next and references IRC 2021 where it applies.

Start with step 1: Deck Material

Which deck calculator should I use first?

Start with the Deck Material Calculator — it converts length, width, and joist spacing into exact board, joist, and footing counts, then feeds those numbers into the cost, structural, and stair calculators. Most homeowners complete a full plan in under 15 minutes using the 7-step path.

The 7-step path

One calculator at a time, in the order they connect

Each step uses values from the previous one. Most homeowners finish in ~10 minutes. Click any step to start there.

  1. Deck Material Calculator

    Calculate exact decking boards, joists, beams, posts, footings, and fasteners for your deck — IRC 2021 compliant.

    Live

  2. Joist Span Calculator

    Maximum joist span for any size, species, and spacing — directly from IRC 2021 R507.6 tables.

    Live

  3. Deck Beam Span Calculator

    Maximum beam span (post-to-post) by size, ply, species, and tributary load — straight from IRC R507.5 / DCA-6.

    Live

  4. Deck Footing Calculator

    Footing diameter, depth, concrete volume, and bag count — IRC R507.3 sized + frost depth lookup for all 50 states.

    Live

  5. Deck Stair Calculator

    Risers, treads, stringer hypotenuse, and BoM for any deck height — IRC 2021 R311.7 compliant with auto handrail + landing-pad sizing.

    Live

  6. 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.

    Live

  7. Deck Cost Calculator

    Estimate full deck project cost: materials, labor, permits, and per-square-foot pricing for any size and material.

    Live

Other paths

All 121 calculators →

Frequently asked

About this path

Which deck calculator should I use first?
Start with the Deck Material Calculator. It establishes your deck's footprint and board count, which every downstream calculator (joist span, beam span, footings, stairs, cost) uses as input.
How long does deck planning take with DeckMath?
Most homeowners finish the 7-step path in 10–15 minutes. Contractors with site dimensions ready usually finish in under 5 minutes per deck.
Are the planning calculators IRC 2021 compliant?
Yes. Joist Span (R507.6), Beam Span (R507.5), Footings (R507.3), and Stairs (R311.7) all validate against published IRC 2021 tables and display compliance badges with the relevant code section.
Do I need an engineer if I follow the 7-step path?
For decks under 200 sqft and 6 ft of height, the IRC 2021 prescriptive path covers code compliance. For hot-tub loads, cantilevers over 2 ft, multi-level decks, or commercial work, the calculators flag engineer review.