Quickly determine if your joist or rafter spans meet the 2021 IRC requirements using our easy-to-use Span & Spacing Calculator. Simply select your member type, size, species, spacing, and span length to instantly check compliance. Perfect for preliminary planning—ensure your design aligns with code before consulting your licensed engineer.

IRC Span & Spacing Calculator (2021)

Member Type: Floor Joist Deck Joist Ceiling Joist Roof Rafter

Live Load for Ceiling Joist: 10 psf (No Storage) 20 psf (Limited Storage)

Snow Load for Rafter: 20 psf 30 psf

Size: 2×6 2×8 2×10 2×12 Species/Grade: Southern Pine #2 Douglas Fir-Larch #2 Hem-Fir #2 Spacing (o.c.): 12″ 16″ 19.2″ 24″ Span Length (ft): Span Length (in): Calculate

Note: Assumes standard dead loads per IRC tables (10 psf for floors/decks, 5 psf for ceilings, 10 psf for rafters). This tool is for estimation only and does not replace a licensed engineer’s review.

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