Significant Wave Height (Hs) is the average height of the highest one-third of waves measured over a given period. It is the standard oceanographic measure used across wave models like SWAN and ECMWF.
Why the highest third?
Hs closely matches what an experienced observer would visually estimate as the wave height. Smaller ripples are excluded because they don't reflect the meaningful energy in the sea state.
Important to remember
- Individual waves can be significantly larger than Hs — some up to twice the value.
- Hs is a deep-water or model-grid value; the surf height you see at the beach depends on nearshore effects.
- Our nearshore SWAN model translates Hs into a realistic breaker height at the spot.