The code is developed in cooperation between the countries around the Baltic Sea to provide a common terminology.
The general formula is AB SB TB KB.
AB - Amount and arrangement of sea ice
0 - Ice free.
1 - Open water – concentration less than 1/10.
2 - Very open pack ice - concentration 1/10 to less than 4/10.
3 - Open pack ice – concentration 4/10 to 6/10.
4 - Close pack ice - concentration 7/10 to 8/10.
5 - Very close pack ice - concentration 9/10 to 9+/10. *
6 - Compact pack ice, including consolidated pack ice – concentration 10/10.
7 - Fast ice with pack ice outside.
8 - Fast ice.
9 - Lead in very close or compact pack ice or along the fast ice edge / Unable to report.
* 9+/10 means ice concentration 10/10 with minor leads.
SB - Stage of development
0 - New ice or dark nilas (less than 5 cm thick).
1 - Light nilas (5-10 cm thick).
2 - Grey ice (10-15 cm thick).
3 - Grey-white ice (15-30 cm thick).
4 - White ice, first stage (30-50 cm thick).
5 - White ice, second stage (50-70 cm thick).
6 - Medium first year ice (70-120 cm thick).
7 - Ice predominately thinner than 15 cm with some thicker ice.
8 - Ice predominately grey-white (15-30 cm) with some ice thicker than 30 cm.
9 - Ice predominately thicker than 30 cm with some thinner ice / No information or unable to report.
TB - Topography or form of ice
0 - Pancake ice, ice cakes, brash ice – less than 20 m across.
1 - Small ice floes – 20-100 m across.
2 - Medium ice floes – 100-500 m across.
3 - Big ice floes – 500-2000 m across.
4 - Vast or giant ice floes – more than 2000 m across – or level ice.
5 - Rafted ice.
6 - Compacted slush or shuga, or compacted brash ice.
7 - Hummocked or ridged ice.
8 - Thaw holes or many puddles on ice.
9 - Rotten ice / No information or unable to report.
KB - Navigation conditions in ice
0 - Navigation unobstructed.
1 - Navigation difficult or dangerous for wooden vessels without ice sheating.
2 - Navigation difficult for unstrengthened or low-powered vessels built of iron or steel. Navigation for wooden vessels even with ice sheating not advisable.
3 - Navigation without icebreaker assistance possible only for high-powered vessels of strong construction and suitable for navigation in ice.
4 - Navigation proceeds in lead or broken ice-channel without assistance of an icebreaker.
5 - Icebreaker assistance can only be given to vessels suitable for navigation in ice and of special size.
6 - Icebreaker assistance can only be given to vessels of special ice class and of special size.
7 - Icebreaker assistance can only be given to vessels after special permission.
8 - Navigation temporarily closed.
9 - Navigation has ceased / Unknown.