Guide · Fixed wall + free tip
Cantilever beam deflection
Balconies, eaves, canopy arms and overhanging decks: fixed at the wall, free at the tip. Everything peaks at the ends — deflection at the tip, moment at the wall.
Formulas
Tip P: δ = PL³/3EI @ tip · Mwall = −PL
P at a from wall: δP = Pa³/3EI · δtip = Pa²(3L−a)/6EI
Full UDL: δ = wL⁴/8EI @ tip · Mwall = −wL²/2
P at a from wall: δP = Pa³/3EI · δtip = Pa²(3L−a)/6EI
Full UDL: δ = wL⁴/8EI @ tip · Mwall = −wL²/2
The 16× rule
PL³/3EI is 16× the simply supported PL³/48EI for identical P, L, E, I. A joist that works at 12 ft as a simple span may only cantilever ~4–5 ft. Size cantilevers by deflection (L/180) first, strength second.
The wall connection is the design
The wall moment −PL (or −wL²/2) must go somewhere: back-span anchorage, a moment frame, or a properly embedded support. A cantilever is only as fixed as its connection — when in doubt, the calculator's propped or simply supported result is the honest fallback, not this page.