Wave period: what the seconds mean for surf

What period is

Period is the time between two wave crests as they pass one point, in seconds. Forecasts call it the swell period or the wave period. It sits next to the wave height, and it tells you more.

A long period means a big storm made the swell far out at sea. Those waves travel for days and keep their power. When they reach shallow water, they stand up taller and break harder than short-period waves of the same height.

Try it

Set the buoy height and the period. The answer is the face height at an open beach break, from the same formula the BarrelFare forecast uses.

A rough guide

• Under 9 seconds: wind swell. Made by wind close by. Short, crowded waves that crumble.
• 9 to 12 seconds: mid-period swell. Good shape on most breaks.
• 13 seconds and up: groundswell. Lined-up sets with gaps between them, and real power.

Long period is not always better. A big groundswell can be too much for a beginner, and it closes out some beaches. Long-period swell also bends around headlands more, so it reaches breaks that a short swell misses.

Where you see it on BarrelFare

Every spot forecast shows the period next to the face height for each hour, and the score already counts it. A 4 ft swell at 16 seconds scores as the bigger, stronger wave it is.

How to read a surf report and forecast