Deck Joist Span Calculator
Three inputs, two outputs. No account, no guesswork—numbers load from our transcribed DCA 6 JSON.
Deck joist span calculator
Pick species group, joist size, and spacing. Results come straight from AWC DCA 6-15 Table 2.
Use the lesser of the table overhang and one-fourth of the actual joist span (L/4). Ledger and guard-post members must be at least 2x8 nominal per DCA 6.
Calculator assumptions
40 psf live load, 10 psf dead load, No. 2 grade, wet service, L/360 main-span deflection. Overhang limited by table value and L/4. Not for hot tubs, snow above 40 psf, or roofed decks.
FAQ
Why does overhang sometimes rise when spacing gets wider?
AWC notes that overhang deflection under a point load improves when the main span shortens. Wider spacing often shortens the allowable main span, which can allow a slightly longer overhang. You still must respect L/4.
Can I use this for a covered deck?
No. Roof loads and drifting snow are outside DCA 6 Table 2. Ask an engineer.
Need the full grid? Open the deck joist span chart.