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Swell Category Table
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Swell Categories

(For more info, go to the Swell Rating System)

This table groups waves into categories based on the size and period of the pure underlying swell. To use this table, select a buoy reading you wish to decipher. For exa.cgie, say your local buoy indicates swell of 6 ft @ 14 secs. Using this table, go to the '14 sec' column, then work your way down the column until you find 6 ft. Then traverse tot he left. You'll find this is a Category 3 swell, capable of producing waves 7.5-10.0 ft. Taking it a step further, you can then expect that any swell with a combination of swell size and period greater than 8.3 ft @ 9 secs up to 3.0-3.9 ft @ 25 secs could produce such a wave, because they are all within the range of a Category 3 swell. The interaction of a primary swell swell and secondary swell or lesser period waves can make waves higher than stated below.

Category Wave Face Height * Swell Height & Period
7 sec 9 sec 11 sec 13 sec 14 sec 17 sec 20 sec 25 sec
0 0 - 2.5 ft <3.6 ft <2.8 ft <2.3 ft <1.9 ft <2 ft <1.5 ft <1.3 ft <0.9 ft
1 2.5-5 ft 3.5-7.1 ft 2.8-5.5 ft 2.3-4.5 ft 1.9-3.8 ft 2-3.9 ft 1.5-2.9 ft 1.3-2.4 ft 1.0-1.9 ft
2 5-7.5 ft >7.2 ft 5.6-8.3 ft 4.6-6.8 ft 3.9-5.7 ft 4-5.9 ft 3-4.3 ft 2.5-3.7 ft 2.0-2.9 ft
3 7.5-10 ft - >8.3 ft 6.7-9.0 ft 5.8-7.6 ft 6-8.9 ft 4.4-5.8 ft 3.8-4.9 ft 3.0-3.9 ft
4 10-15 ft - - >9.1 ft 7.7-11.5 ft 9-10.7 ft 5.9-8.8 ft 5.0-7.4 ft 4-5.9 ft
5 15-20 ft - - - >11.6 ft 10.8-14.1 ft 8.9-11.7 ft 7.5-9.9 ft 6-7.9 ft
6 20-25 ft - - - - >14.2 ft 11.8-14.7 ft 10-12.4 ft 8.0-9.9 ft
7 25-30 ft - - - - - 14.8-17.6 ft 12.5-14.9 ft 10.0-11.9 ft
8 30-40 ft - - - - - >17.7 ft 15-19.5 ft 12-15.9 ft
9 40-50 ft - - - - - - 20-24.9 ft 16-20 ft
10 >50 ft - - - - - - 25 ft + 20 ft +

* - Average height of the largest 1/3 waves. Measurements in feet from trough to crest. Beaches with size enhancing bathymetry can cause actual wave heights to be up to double the stated size. Scale accordingly using your local knowledge.

 

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