How much could an Age of Sail mast flex?

How much did a ship's mast flex in gusty conditions?

Estimates vary from about six inches to roughly a foot at the masthead, depending on wind, construction, and timber quality.

Claims put masthead movement at roughly a foot each way, though estimates near six inches seem more common. Even a small visible displacement at the top represents limited flex across a very long spar. The safe amount depended on wind strength, workmanship, and the species and quality of timber. Prime Norwegian spruce or fir could absorb considerable movement without failing.