What is significant wave height?

Significant wave height (H₁/₃) is the average height of the highest one-third of waves in a given period. It closely matches the wave height a trained observer would estimate by eye, and is the standard metric used in marine forecasts.

Fetch is the unobstructed distance of open water over which the wind blows in a consistent direction. Longer fetch allows wind to transfer more energy to the water, producing larger waves. Coastlines, islands, and shorelines all limit effective fetch.

What is the SMB method?

The Sverdrup-Munk-Bretschneider (SMB) method is an empirical wave forecasting technique developed in the 1940s–1950s. It uses dimensionless fetch and wind speed parameters to predict wave height and period. It is most accurate for fetch-limited, open-ocean conditions with steady wind.

How accurate are these estimates?

SMB predictions are engineering approximations valid for steady, uniform wind over open water. Real-world accuracy is typically ±20–30%. Factors like wind direction changes, swell from distant storms, currents, and bottom topography are not captured by this simplified model.

Does this include shallow-water effects?

No. This calculator estimates deep-water wind-wave growth. It does not model shoaling, refraction, breaking, or seabed effects near shore.

What does wave energy density mean?

Wave energy density (E) is the total mechanical energy (kinetic + potential) per unit surface area, in J/m². It equals ρgH²/8 where ρ is water density, g is gravity, and H is significant wave height. Higher values indicate more energetic sea states that impose greater loads on structures.

Wave Height Calculator

Enter wind speed and fetch distance to calculate significant wave height, period, speed, wavelength, and energy using the Sverdrup-Munk-Bretschneider (SMB) method.

Wave Inputs

Wind Speed

Sustained 10-m wind speed over water

Fetch Distance

Unobstructed open-water distance

Result Height Units

Enter wind speed and fetch, then click Calculate Waves.

Summary

This calculator applies the Sverdrup-Munk-Bretschneider (SMB) empirical method to predict fetch-limited ocean wave properties from wind conditions. Given wind speed and the unobstructed water distance (fetch), it computes significant wave height (H₁/₃), peak wave period, phase speed, deep-water wavelength, and wave energy density. Results reflect the statistical average of the highest one-third of waves, which is the standard marine forecast metric.

How it works

Enter the sustained wind speed in knots, m/s, km/h, or mph.
Enter the fetch distance — the unobstructed open-water length the wind blows across — in km, nautical miles, or miles.
The calculator applies the SMB dimensionless fetch equations to derive significant wave height (H₁/₃) and peak period (Tp).
Derived quantities (phase speed, wavelength, energy density) are computed from linear wave theory.
Results update instantly; switch units at any time.

Use cases

Marine weather forecasting and coastal engineering planning.
Estimating wave conditions for offshore platform design.
Sailing and boating route safety assessment.
Educational demonstrations of fetch-limited wave growth.
Coastal erosion and sediment transport research.
Harbor and breakwater design feasibility checks.

Frequently Asked Questions

Last updated: 2026-06-11 · Reviewed by Nham Vu