Significant Wave Height Calculator
Compute significant wave height from spectrum variance (Hs = 4√m₀) or estimate it from wind speed and fetch via JONSWAP.
m₀ is the integral of the wave energy spectrum S(f) over all frequencies. Typical ocean swells: 0.1–5 m².
Neutral wind speed at 10 m above sea surface. Beaufort 6 ≈ 12 m/s; gale ≈ 20 m/s.
Distance over which the wind blows unobstructed. Coastal bay: 10–50 km; open ocean: 500+ km.
WMO Sea State Scale Reference
| Code | Description | Hs range (m) |
|---|---|---|
| 0 | Glassy / calm | 0 |
| 1 | Rippled | 0 – 0.1 |
| 2 | Wavelets | 0.1 – 0.5 |
| 3 | Slight | 0.5 – 1.25 |
| 4 | Moderate | 1.25 – 2.5 |
| 5 | Rough | 2.5 – 4.0 |
| 6 | Very rough | 4.0 – 6.0 |
| 7 | High | 6.0 – 9.0 |
| 8 | Very high | 9.0 – 14.0 |
| 9 | Phenomenal | > 14.0 |
Summary
Compute significant wave height from spectrum variance (Hs = 4√m₀) or estimate it from wind speed and fetch via JONSWAP.
How it works
- Choose a calculation method: Spectrum (from m₀) or JONSWAP (from wind speed and fetch).
- For the Spectrum method, enter the zeroth spectral moment m₀ in m².
- For the JONSWAP method, enter the 10 m wind speed (m/s) and the fetch distance (km).
- Click Calculate to compute significant wave height Hs in meters.
- Review the intermediate values and formula details shown beneath the result.
Use cases
- Coastal and offshore engineering design for platforms and breakwaters.
- Maritime route planning and vessel safety assessments.
- Research and education on ocean wave dynamics.
- Checking JONSWAP fetch-limited wave growth estimates.
- Converting wave spectrum output from models (WAVEWATCH III, SWAN) to Hs.
- Estimating wave conditions from measured or forecast wind data.
Frequently Asked Questions
Last updated: 2026-06-15 ·
Reviewed by Nham Vu