Calculate the maximum safe load for a shelf based on span, wood species, and thickness.
This uses the simply-supported beam formula for a uniformly distributed load. E is the modulus of elasticity (stiffness) of the wood, and I = (depth × thickness³) / 12 is the second moment of area.
The deflection limit controls how much the shelf can bow. L/360 means the midpoint can deflect at most 1/360th of the span — about ⅛″ on a 48″ shelf — which is barely perceptible. L/240 is the minimum for most building codes.
Actual capacity depends on wood quality, grain direction, and connection details. These results are estimates — always apply engineering judgement for structural applications.