Wave Height & Period Calculator

Fetch-limited means the wind has blown long enough that waves would keep growing if there were more open water to blow across, but the shoreline or an opposing coast cuts the fetch short first. Duration-limited means the opposite -- there is plenty of open water available, but the wind simply hasn't been blowing long enough yet to develop the waves that fetch alone would allow. The calculator checks both limits and reports whichever produces the smaller (more restrictive) wave height.

Once the wind has blown long enough for a given fetch to become the binding constraint, the sea state becomes "fully developed" for that fetch -- waves have extracted about as much energy from the wind as that stretch of open water allows, and further duration no longer matters because fetch, not time, is now what's limiting growth. This mirrors real ocean behavior, where a fully developed sea stops growing regardless of how much longer a steady wind continues.

Significant wave height (Hs) is a statistical average of the highest third of waves in a sea state, not the single largest wave you might encounter. The roughly 1.86x multiplier used here for maximum wave height is a commonly cited estimate for the largest wave in a fully developed sea over a typical observation period, but individual freak waves can exceed it -- mariners and coastal engineers generally treat it as a planning figure, not a hard ceiling.

No -- it uses the deep-water SMB formulation, which assumes open water far from shore with no depth-limited wave breaking or shoaling. Coastal areas, shallow bays, and variable bathymetry all modify real wave growth in ways this idealized fetch-and-duration model does not capture, so results near a shoreline should be treated as a rough starting estimate rather than a site-specific forecast.