Cruise sea states explained
The Douglas sea state scale rates the sea from 0 (flat calm) to 9 (phenomenal) by wave height. It is the scale MyCruiseForecast uses for wave heights on sea days and in port.
The Douglas scale in feet and meters
| State | Description | Wave height | What it feels like |
|---|---|---|---|
| 0 | Calm (glassy) | 0 | Mirror-flat water, no wave motion at all. |
| 1 | Calm (rippled) | 0 to 0.1 m0 to 0.3 ft | Barely a ripple, a pool-deck kind of day. |
| 2 | Smooth | 0.1 to 0.5 m0.3 to 1.6 ft | Small wavelets; most guests will not notice any motion. |
| 3 | Slight | 0.5 to 1.25 m1.6 to 4.1 ft | Small waves and a light swell, with little motion felt. |
| 4 | Moderate | 1.25 to 2.5 m4.1 to 8.2 ft | Some motion, mostly felt forward and on high decks. |
| 5 | Rough | 2.5 to 4 m8.2 to 13.1 ft | A noticeable roll. Cabins low and midship feel steadiest. |
| 6 | Very rough | 4 to 6 m13.1 to 19.7 ft | Expect real motion; open decks may close. |
| 7 | High | 6 to 9 m19.7 to 29.5 ft | Heavy seas. Strong motion throughout the ship; itineraries may be altered. |
| 8 | Very high | 9 to 14 m29.5 to 46 ft | Severe conditions. Ships normally change course to avoid them. |
| 9 | Phenomenal | Over 14 mOver 46 ft | Extreme seas, rarely forecast; cruises route around them. |
What the number measures
MyCruiseForecast reports significant wave height: the average of the highest third of waves. Occasional waves run larger. The scale describes the sea surface only. Wind, swell period and the size of your ship decide how much of it you actually feel.
Which levels matter for most cruisers
States 0 to 3 are what most cruises see most of the time, and most guests feel little or no motion. State 4 brings some movement, mostly at the front of the ship and on high decks. From state 5 up you will notice a roll, and from state 6 open decks can close. Larger ships generally move less than smaller ones at the same wave height.
Choosing a cabin for less motion
Cabins low in the ship and near the middle feel the least movement. If you are prone to motion sickness, that location matters more on routes with long open-water stretches, such as transatlantic crossings and some sea days between island groups.
See typical seas for your route
Every port page lists typical and rougher-day wave heights by month, and each sailing page shows approximate seas on its sea days. For a live forecast as your date gets closer, check your sailing.
Questions
What sea state is too rough for a cruise?
There is no published cutoff. Captains weigh wave height, swell direction, wind and conditions at the next port, and may change speed or route, or skip a port. Sea states 7 and above are rare on cruise itineraries because ships route around them.
What is significant wave height?
It is the average height of the highest third of waves in a given period. Individual waves can be noticeably larger, so the number describes the typical rough end of what you will see, not the single biggest wave.
Does sea state decide whether I will get seasick?
Wave height is one factor. Swell period and direction, where you are on the ship and your own sensitivity matter too. A long, low swell can feel gentler than shorter, steeper waves of the same height.
Where is the calmest part of the ship?
Low decks near the middle of the ship move the least. Upper decks and the bow and stern feel more of the motion.