Douglas Sea Scale

The Douglas sea scale is a scale which measures the height of the waves and also measures the swell of the sea.

The scale is very simple to follow and is expressed in one of 10 degrees.

The Douglas sea scale, also called the “international sea and swell scale”, was devised in 1921 by Captain H.P. Douglas, who later became vice admiral Sir Percy Douglas and hydrographer of the Royal Navy.

Its purpose is to estimate the roughness of the sea for navigation.

The scale has two codes: one code is for estimating the sea state, the other code is for describing the swell of the sea.

The Degree value has an almost linear dependence on the square root of the average wave Height below.

OceanWave Beaufort
DegreeDescriptionHeight (m)Height (ft)
0Calm (Glassy)no wave
1Calm (rippled)0–0.100.00–0.33
6Very rough4.00–6.0013.1–19.7
8Very high9.00–14.0029.5–45.9
0No swell
1Very Low (short or average and low wave)
2Low (long and low wave)
3Light (short and moderate wave)
4Moderate (average and moderate wave)
5Moderate rough (long and moderate wave)
6Rough (short and high wave)
7High (average and high wave)
8Very high (long and high wave)
9Confused (wavelength and height indefinable)

Wave length and height classification


  • Short wave: < 100 mt
  • Average wave: 100–200 mt
  • Long wave: > 201 mt

Wave height

  • Low wave: < 2 mt
  • Moderate wave 2–4 mt
  • High wave > 4.01 mt
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