Depth beats width, cubed

Double a beam’s depth and its deflection drops 8-fold. Double its width and it only halves.

Why it works

Bending stiffness follows I = b·h³/12 — depth enters cubed, width linearly. Joists stand on edge for a reason.

Do it exactly

Estimate with the rule, then check it against the calculator that models it properly.

Open Beam Bench — deflection & stress →

More in Mechanical

• The bolt-torque shortcutTightening torque ≈ 0.2 × preload × bolt diameter (dry steel).
• Torque mostly fights frictionRoughly 90% of tightening torque is lost to friction; only ~10% actually stretches the bolt.
• Deflection limits: span/250Keep beam deflection under span/250 generally, span/360 where people will notice a bouncy floor.
• Keep water at 1–2.5 m/sSize pipes so water flows between about 1 and 2.5 m/s.

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