Beam & Joist Span Calculator
Check whether a floor joist size and spacing can carry a given span using the IRC floor joist span table for SPF #2, with the maximum allowed span. Calculates in your browser.
Maximum allowed span
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Show the math
The maximum span comes from IRC Table R502.3.1(2), floor joist spans for spruce-pine-fir #2:
pass when required span ≤ maximum allowed span
Spans are the code table's values for SPF #2 lumber in residential living areas: 40 psf live plus 10 psf dead, with deflection limited to L/360. Other species, grades, heavier dead loads, sleeping-area (30 psf) tables, and concentrated loads change the answer, and your local code may differ. This is a planning check, not an engineering approval: have your building department or 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 the IRC floor joist span table for SPF #2, 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 reads IRC Table R502.3.1(2) for SPF #2 at 40 psf live and 10 psf dead; it is not an engineering approval, and that load and species grade 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 up to 12 ft 3 in, so a 12-foot span passes and a 12½-foot span does not.
Last updated .
Frequently asked questions
How far can a 2×8 joist span?
For SPF #2 at 16-inch spacing in a residential living area, 12 ft 3 in per IRC Table R502.3.1(2). The tool looks this up and compares it to your span.
What load do the tables assume?
The IRC table for residential living areas: 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 reads the code table for one species and grade, but your building department or a professional should verify any structural framing.
Do you store my numbers?
No. Everything is calculated locally in your browser.
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