(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.