An ice climbing rating system is an attempt to help climbers understand the physical difficulty of a given route. The most common rating system in North America is the WI scale (which stands for “water ice”) and unlike rock climbing ratings it’s based on the overall steepness of a pitch rather than the single most difficult move. You may also see AI ratings (which stands for “alpine ice”) if ice climbing in an alpine environment. Though the AI scale correlates directly to WI the ice tends to be very different in character due to the formation process of ice in the alpine: alpine ice is generally more homogenous and smooth whereas water ice can be highly featured and aerated. Also, to make things even more complicated, New England also uses it’s own NE rating system (which stands for, you guessed it “New England”), often directly correlating with the WI scale.
The WI grading system is historic and originated without the benefit of modern ice tools, plus with the popularity of ice climbing now it’s not uncommon to have a well-traveled route making for significantly easier succeeding ascents. Also, grades often do not accurately factor in ice quality, protection opportunities and the mental challenge. It is not uncommon to have a cold, brittle WI4 that can feel more challenging than a well featured WI5 with a warmer, plastic like ice. Here is a quick breakdown of the WI grades:
WI1: Very low angle ice where no ice tools or possibly only one tool for balance would be required. This terrain may be up to 45°.
WI2: Low angle ice up to 60° with lots of secure stances. Can often be climbed with a single ice tool though two tools provide better security, these routes are ideal for beginners to practice and learn fundamental crampon and ice tool techniques with a focus on balance.
WI3: Moderate angle ice around 70°, possibly with a couple of bulges or short, steeper sections around 80°. Despite the possibility of bulging sections and continuous frontpointing, there should be ample opportunities for rests and comfortable stances. This is typically a fun, achievable grade for beginner ice climbers and a likely first lead grade.
WI4: Sustained stretches of 80° icenear-vertical with possibly limited rest positions. Good technique becomes essential for efficient climbing and avoiding pumping out.
WI5: Sustained vertical ice at 90°. Pitches are often long and challenging, possibly a delicate pillar that requires delicate, precise placements. This grade is considered advanced and climbers must use both good technique and have a level of upper body, grip and core strength.
WI6: Sustained vertical and overhanging ice with difficult/tricky sections. Ice can be thin or have unique features that require creative climbing techniques.