Floor Joist Span Calculator
Look up maximum floor joist spans for Southern Pine No.2 from a published span-table excerpt.
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What this tool does
Look up maximum floor joist spans for Southern Pine No.2 from a published span-table excerpt. Scope is deliberately narrow: one species/grade (Southern Pine No.2), four sizes, three spacings, living-area loads (40 psf live + 10 psf dead, L/360). Other species, grades and load cases need the full AWC/IRC tables or an engineer.
How to use the Floor Joist Span Calculator
- Enter or select joist size (southern pine no.2).
- Enter or select joist spacing.
- Enter or select your planned span in ft.
- Read the calculated result; change any measurement to compare alternatives.
Formula
table lookup: maximum span for Southern Pine No.2 at 40 psf live + 10 psf dead load, L/360 deflection (published SFPA Table 2 basis)
- size
- Joist size (Southern Pine No.2)
- spacing
- Joist spacing
- span
- Your planned span (ft, before metric conversion)
Scope is deliberately narrow: one species/grade (Southern Pine No.2), four sizes, three spacings, living-area loads (40 psf live + 10 psf dead, L/360). Other species, grades and load cases need the full AWC/IRC tables or an engineer.
Worked example
For floor joist span calculator, the following measurements illustrate the exact method: Joist size (Southern Pine No.2): 2x6; Joist spacing: 12; Your planned span: 12.
Inputs
- Joist size (Southern Pine No.2)2 × 6
- Joist spacing12 in on centre
- Your planned span12 ft
Result
- Maximum allowable span10.25 ft
- Maximum span10 ft 3 in
- Your planned span12 ft
- CheckPlanned span EXCEEDS the table value — upsize or add support
Southern Pine No.2 max floor joist spans (40/10 psf, L/360)
| Size | 12 in o.c. | 16 in o.c. | 24 in o.c. |
|---|---|---|---|
| 2x6 | 10-3 | 9-4 | 7-7 |
| 2x8 | 13-6 | 11-10 | 9-8 |
| 2x10 | 16-2 | 14-0 | 11-5 |
| 2x12 | 19-1 | 16-6 | 13-6 |
Results explained
- Maximum allowable span
- Maximum allowable span from the formula above, expressed in ft before metric conversion. Scope is deliberately narrow: one species/grade (Southern Pine No.2), four sizes, three spacings, living-area loads (40 psf live + 10 psf dead, L/360). Other species, grades and load cases need the full AWC/IRC tables or an engineer.
- Maximum span
- Maximum span from the formula above. Scope is deliberately narrow: one species/grade (Southern Pine No.2), four sizes, three spacings, living-area loads (40 psf live + 10 psf dead, L/360). Other species, grades and load cases need the full AWC/IRC tables or an engineer.
- Your planned span
- Your planned span from the formula above, expressed in ft before metric conversion. Scope is deliberately narrow: one species/grade (Southern Pine No.2), four sizes, three spacings, living-area loads (40 psf live + 10 psf dead, L/360). Other species, grades and load cases need the full AWC/IRC tables or an engineer.
- Check
- Check from the formula above. Scope is deliberately narrow: one species/grade (Southern Pine No.2), four sizes, three spacings, living-area loads (40 psf live + 10 psf dead, L/360). Other species, grades and load cases need the full AWC/IRC tables or an engineer.
Frequently asked questions
Southern Pine No.2 at 16 in on centre: 11 ft 10 in under living-area loads (40 psf live, 10 psf dead, L/360) per the published SFPA span tables. At 12 in spacing it reaches 13 ft 6 in.
14 ft for Southern Pine No.2 under the same load case. The pre-2013 tables allowed more — Southern Pine design values were reduced in 2013, which is why older charts disagree.
Span tables are species- and grade-specific. Rather than publish numbers we cannot source for every species, this tool excerpts one well-documented table and labels it. Douglas fir, SPF and hem-fir have their own IRC tables.
40 psf is the standard residential living-area live load; L/360 caps deflection at span ÷ 360, the usual floor stiffness limit. Bedrooms may use 30 psf, decks and tile floors often need more.
Yes — a mid-span beam or bearing wall splits one long span into two shorter ones, and each half is checked against the table independently.