Yosemite Decimal System

The Yosemite Decimal System (YDS) is a three-part system for rating the difficulty of hiking, mountaineering, and climbing, used primarily in the United States and Canada. It was first established in the 1950s by members of the Sierra Club in Southern California as an improvement on earlier systems, particularly those more common in Yosemite Valley, and quickly spread across North America.

The Class 5 section of the scale is primarily a system for scaling climbing difficulty, whereas Classes 1 and 2 focus more on the requirements of hiking, trail running, and "scrambling," a kind of hybrid of hiking, climbing, and mountaineering. Class 3 describes easy and moderately challenging mountaineering (i.e. scrambling) with varying levels of difficulty and danger. Class 4 is an "intermediate" level for more challenging mountaineering, roughly corresponding to the "PD+" grade of the French IFAS system. Climbers, especially those in the technically demanding grade 5, abbreviate grades 3 and 4 as "3rd" and "4th" respectively.

Originally, this was a one-part classification system. The categories "grade" and "protection" were added later. The new categories cannot be applied to all climbing, and their use varies widely. Grade" describes the time required to complete a climb, while "protection" describes the availability and quality of points on a climb (hereafter "belay points") where a climber should use belay devices.

Class 5 is divided into subclasses; currently the subclasses 5.0 to 5.15 are distinguished. The classifications above 5.9 are further subdivided, e.g. there is 5.10b or 5.15c. When a full YDS classification is described, the grade of the class is placed after it, followed by the fuse, resulting in a construct such as "5.10b VI R". Often the grade is omitted and only the class and fuse are used. If there is no agreement on the amount of belaying required on a route, this is also omitted.

While primarily a free climbing system was described, there were occasional additions of a technical climbing system described as A0 ... A5. For example, the North American face of El Capitan is classified as "5.8 VI A5" using a mixed system.

Grade

The YDS grade system includes an optional Roman numeral-enriched system that incorporates the length and difficulty of a route.

The grade is more relevant for mountaineers and climbers on big rock faces and is often not mentioned for short tours.

Other systems

There are other classification systems. They are summarized in the article Difficulty Scale (Climbing).