How far can a 2x10 span?

A 2x10 Douglas Fir #2 floor joist at 16 inches OC can span approximately 16 feet for residential live loads (40 psf). At 12 inches OC, it spans ~18 feet. Ceiling joists (lighter load) can span 21+ feet. Always check IRC span tables for your exact species and grade.

What's the difference between #1 and #2 lumber?

#1 grade has fewer knots and defects, making it 10-15% stronger. A #1 2x10 might span 17.5 feet where a #2 only spans 16 feet. #1 costs 15-30% more but is worth it for critical long spans or heavy loads.

🪵 Lumber Span Calculator

Lumber Size

Species & Grade

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Application

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Maximum allowable span (IRC)

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📏 Lumber Span Basics

Span vs Load: Floor joists carry more load (people, furniture) than ceiling joists (just drywall), so they span shorter distances for the same lumber size.

Quick Reference Span Table (Douglas Fir #2, 16" OC)

Size	Floor Joist	Ceiling Joist	Roof Rafter
2×6	9' 11"	15' 7"	12' 4"
2×8	13' 1"	20' 8"	16' 4"
2×10	16' 5"	21' 0"	20' 3"
2×12	19' 1"	21' 0"	21' 0"

Spacing Matters: Closer spacing = longer spans. A 2×10 at 12" OC spans 18' for floors, but only 16.5' at 16" OC.

#1 vs #2 Grade: #1 grade adds ~10% to span. If #2 spans 16', #1 spans ~17.5'. Costs 20-30% more.

Common Mistake: Don't confuse nominal size with actual. A "2×10" is actually 1.5" × 9.25". The span tables account for this.