This calculator uses the L/360 deflection limit to find the maximum load. Recommended Maximum Load Formula Using the deflection formula for a simply supported beam with a uniformly distributed load: Max load (lbs) = (384 × E × I) / (5 × L³) × (L/360)Free shelf span calculator for accurate shelving design. Calculate maximum shelf length, load capacity, and deflection for wood shelves, plywood, and MDF. Switch between design and check modes, then download tidy reports as needed. Choose units first; conversions run automatically. 125") sag is acceptable for a 36" shelf. Consider the visual impact - even small amounts of sag are very. Definition: The Shelf Load Capacity Calculator estimates the maximum weight (L C) a shelf can support using the formula L C = 4 3 × M S × W × T 2 L, based on material strength (M S), shelf width (W), thickness (T), and length (L).