Deflection (L/360)

Definition

L/360 is a stiffness target: deflection no greater than the span divided by 360. On a 36 in shelf that is 0.10 in (2.5 mm). For a simply supported rectangular shelf with uniform load, δ = 5WL³ / (384EI) where W is the total load, and I = bh³/12. Thickness dominates because it is cubed. MDF often fails L/360 sooner than plywood of the same size because its modulus E is lower. Brackets and fixed ends sag less than this conservative model.

Calculators that use this

• Fine woodworking & cabinetry

  Shelf Sag (Load Bearing) Calculator

  Estimate shelf deflection from span, thickness, depth, material and load, and check a simple L/360 stiffness rule.

• Fine woodworking & cabinetry

  Wood Movement / Expansion Estimator

  Estimate seasonal width change of a board from species, flatsawn vs quartersawn cut, and the change in moisture content.