Universal Converter Pro

What is a Floor Joist Span?

A floor joist's "span" is the maximum horizontal distance it can extend between two points of support (like a foundation wall and a central beam) without excessive bending or sagging. This calculator uses pre-computed data from standard building code span tables to give you a reliable answer.

The calculation depends on the joist's size (deeper is stronger), the wood's inherent strength (its Fiber Bending or "Fb" value), the spacing between joists, and the acceptable "deflection" (how much it can bend under a load). A safe span is critical for a floor that feels solid and meets safety regulations.

Common Framing Lumber: Species & Use

How to Use the Floor Joist Calculator

1. Wood Species & Grade: Select the type of wood you are using. Stronger woods like Southern Pine can span longer distances.
2. Joist Size: Choose the nominal size of your lumber (e.g., 2x8, 2x10). Taller joists are significantly stronger.
3. Joist Spacing: Select the on-center spacing for your joists. Closer spacing results in a stronger floor.
4. Deflection Limit: Choose the stiffness standard. L/360 is standard for living areas, while L/480 is recommended for floors under tile to prevent cracking.
5. Calculate: Instantly find the maximum distance your selected joist can safely span between supports.

Max Span vs. Joist Size (Douglas Fir #2, 16" O.C.)

Illustrates how span increases dramatically with joist depth

Frequently Asked Questions (FAQ)

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