Shelf Sag/Deflection Calculator
Uniform Load Deflection
Calculate shelf sag under evenly distributed weight
Formula
Deflection = (5 x w x L^4) / (384 x E x I) | I = (b x h^3) / 12 | where w = load/inch, L = span, E = MOE
Frequently Asked Questions
How much sag is acceptable?
A common rule of thumb is that deflection should be less than 1/50 of the span (L/50). For a 36-inch shelf, that means less than 0.72 inches. For fine furniture, aim for L/200 or less.
How can I reduce shelf sag?
Increase thickness, use a stiffer material, reduce span (add a center support), add a front edge band for extra rigidity, or reduce the load.
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