Shelf Span Calculator

Calculate the maximum safe span for a shelf based on its material and expected load.

Safe Span
— inches
Max unsupported length.

Usage Tip

Add a front edge band or a center support to stiffen a long shelf without going to thicker stock.

THE MATH
safe span = material rating × √(reference load ÷ actual load)
reference load = 20 lbs per linear foot
A shelf sags more as it gets longer or carries more weight. Each material has a safe span at a reference load, and the span shrinks with the square root of any heavier load.
Pick the shelf material and thickness, then enter the load in pounds per linear foot (books are roughly 20 to 30).
The result is the maximum span between supports.
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The calculators and tools on Formula Factory are provided for general guidance and informational purposes only. Results are estimates based on standard formulas and the values you enter — they do not constitute professional engineering, electrical, or architectural advice. Always verify calculations with a qualified professional before making decisions for any safety-critical, code-compliance, or commercial application. Formula Factory makes no representations or warranties as to the accuracy or completeness of any result, and accepts no liability for errors, omissions, or any outcomes arising from reliance on this information.