Deck calculator
Size deck joists and beams straight from the American Wood Council's DCA6 prescriptive deck guide - the residential deck tables most building departments accept.
First deck? How far can a deck joist span? walks through why decks use a different table from indoor floors, how the published overhang works, and how the joist span drives the beam.
Deck joists
Every figure on this page is read straight from DCA6 at its own conditions: No. 2 grade lumber, 40 psf live plus 10 psf dead, L/360 deflection, and wet-service (exterior) values. A deck outside those conditions is not this table.
Allowable overhang beyond the beam: 2′-0″ (never more than one quarter of the actual back-span).
Deck beams
Pick the total joist span the beam carries (joists framing one side) and a built-up or solid beam size to read its maximum beam span.
Source: DCA6 - Prescriptive Residential Wood Deck Construction Guide, 2012 - Table 2 (deck joists) and Table 3A (deck beams). Published by American Wood Council.
Edition: These values are transcribed from the 2012 edition of DCA6. The AWC has since published newer editions, and adopted requirements vary by jurisdiction - confirm against the edition your local building department uses before relying on a span.