Wood Screw Withdrawal Calculator

Estimate how much pull-out force a wood screw can resist, from the screw gauge, the wood species, and the depth of thread penetration.

How It Works

The estimate uses the common empirical withdrawal formula P = 2850 × G² × D × L, where G is the specific gravity of the wood, D the shank diameter in inches, and L the threaded penetration in inches. It assumes side-grain insertion with a proper pilot hole (about the root diameter of the screw). Withdrawal in end grain is roughly 60% weaker, and a larger pilot hole or an over-driven screw can cut the value sharply — the calculator shows the estimate divided by four as a conservative working load.

Reference values only — always confirm critical fastening decisions against your engineering specification or the fastener manufacturer.

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