Beam & Joist Span Calculator
Check whether a floor joist size and spacing can carry a given span using simplified SPF #2 span tables, with the maximum allowed span. Calculates in your browser.
Maximum allowed span
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Show the math
The maximum span comes from a simplified SPF #2 floor-joist table:
pass when required span ≤ maximum allowed span
Spans assume SPF #2 lumber under a residential floor load of 40 psf live plus 10 psf dead, with deflection limited to L/360. This is an educational estimate, have a professional verify any structural framing. All math runs locally in your browser.
What this does
A joist span calculator checks whether a floor joist size and spacing can carry a given span using simplified SPF #2 span tables, with the maximum allowed span.
How to use it
- Choose the joist size.
- Set the spacing.
- Enter your span.
- See the allowed span and pass or fail.
How it works
The tool looks up the table value for your size and spacing and compares it to your span. It is an educational estimate, not an engineering approval.
assumes 40 psf live + 10 psf dead, L/360
Understanding your result
This is an educational estimate from simplified SPF span tables, not an engineering approval, and it assumes a specific load and species grade that may not match your project. Real spans depend on wood grade, actual loads, and openings, so use it to sanity-check a plan, then confirm anything you will build with a structural table, engineer, or inspector.
Example
A 2×8 SPF #2 at 16-inch spacing spans about 12–13 feet.
Sources & methodology
Last updated .
Frequently asked questions
How far can a 2×8 joist span?
For SPF #2 at 16-inch spacing under a typical residential floor load, about 12–13 feet. The tool looks this up and compares it to your span.
What load do the tables assume?
A common residential floor load of 40 psf live plus 10 psf dead, deflection limited to L/360. Always confirm against your local code.
Is this an engineering approval?
No, it is an educational estimate from simplified tables. Have a professional verify any structural framing.
Do you store my numbers?
No. Everything is calculated locally in your browser.
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