MARITIME – METEOROLOGY & EA TATE CALCULATOR
Douglas Sea State
A precise tool.
What is the Douglas Sea State & How does it work?
The Douglas Sea State Scale, developed in the 1940s, provides a standardized way to describe sea conditions based on the significant wave height observed over a given area. It is widely used by mariners, meteorologists, and naval architects to assess vessel performance and safety. Wave height, measured in metres, is the primary parameter that determines the sea state. The scale ranges from 0 (calm) to 9 (phenomenal), each class representing a range of wave heights and associated surface conditions. Understanding the relationship between wave height and sea state enables better route planning, risk assessment, and design of offshore structures. The following piece‑wise function maps wave height (H) to the corresponding Douglas Sea State (S).
S = \begin{cases}0, & H < 0.1 \\ 1, & 0.1 \le H < 0.5 \\ 2, & 0.5 \le H < 1.25 \\ 3, & 1.25 \le H < 2.5 \\ 4, & 2.5 \le H < 4 \\ 5, & 4 \le H < 6 \\ 6, & 6 \le H < 9 \\ 7, & 9 \le H < 14 \\ 8, & 14 \le H < 20 \\ 9, & H \ge 20 \end{cases}
H = wave height (m) S = Douglas Sea State
Parameters
Result
—
Frequently Asked Questions
What is the range of the Douglas Sea State Scale?
The scale ranges from 0 (calm) to 9 (phenomenal), each class representing different wave heights and surface conditions.
How is the sea state determined using this scale?
Sea state is determined by measuring the significant wave height in meters, which then corresponds to a specific class on the Douglas Sea State Scale.
What does a sea state of 5 indicate according to the Douglas Sea State Scale?
A sea state of 5 indicates moderate waves with some spray and white foam crests. The wave height is typically between 3.0 to 4.9 meters.
Who uses the Douglas Sea State Scale?
Mariners, meteorologists, and naval architects use this scale to assess vessel performance and safety in various sea conditions.
What is the primary parameter for determining the sea state on this scale?
The primary parameter is the significant wave height measured in meters.
Results are for informational purposes only and do not constitute professional advice.