The Climbing&Bouldering Grade System

The Yosemite Decimal System

Five classes of climbing difficulty
The Yosemite Decimal System consists of five general classes, the fifth being subdivided with a decimal notation, but it is generally accepted that some ratings are too high or too low because people want to brag or because the standards among climbers has changed over time, and many people have editorial comments about the YDS.

The class of a route is derived from its "crux" or hardest move. If you hike a class 2 trail from point A to point B, and are required to scale a 20 foot wall of rock (class 4) along the way, then you hiked a class 4 trail regardless of the normal exposure.

The argument that exposure has nothing to do with the class of the climb is not supported by the history of YDS. Exposure was implied in the definition of 4th and 5th class by the use of a rope. Starting in the 5th edition of Freedom, exposure was included in the class descriptions, probably because of the wide variety of techniques being used on the same climbs. In the 6th edition of Freedom, the wording has changed again.

Here are the five classes, where each bullet represents a different opinion as to what the class actually represents. When you are reading a route description or trip report, keep in mind that there may not be general agreement on ratings. The astonishing thing about the email discussion which prompted this expanded definition is that almost everyone thought that almost everyone ELSE agreed with them!

class 1 (used for some peaks that do NOT have trails)

hiking on trail
bikepath
walking, preferably uphill
walking along a clear, well established trail (sidewalk)

class 2

cross country, requiring route finding skills
cross-country, using hands for balance
hiking trail (goes with class 1 is a bike path)
difficult cross-country travel (thick brush, climbing over and around fallen trees, and big talus - hands are used for balance)
the trail is either non-existant or very uneven or intermittent and you may need to put your hand down once in a while for balance

class 3

scrambling on rocks using hands as well as feet
requires use of hands for climbing, rope may be used
I need my hands but might survive a fall
hands? Maybe. (goes with class 1 is a bike path)
rope is necessary only to provide comfort
MUST use your hands for progress but don't need to search for holds nor do you need Real Rock Climbing(TM) techniques

class 4

climbing on steep terrain requiring roped belay
I would die if I fell
hands? Yes! (goes with class 1 is a bike path)
exposed climbing such as a ladder going up the side of a water tank (belays should be used)
use a rope, but don't place protection
rope required to prevent serious injury if a fall occurs
why don't we just ditch Class 4 and call everything 5.0 that used to be Class 4!
you are leading along and it is not too hard and when you get to the end of the lead you notice that you haven't felt motivated to place any protection

class 5

climbing involving technical moves and protective hardware in case of a fall
safety rope (goes with class 1 is a bike path)
thin, exposed climbing, requiring skill (the holds are not obvious to a novice - this is where weird moves such as laybacks, underclings, and evangelical hammerlocks come into play_
leader places protection along the way
Real Rock Climbing(TM) where most people will use a rope (but where some very experienced people won't feel the need) and where serious injury or death is very likely if you take an unprotected fall

class 6 (not actually part of the YDS)

the rope bears the climber's weight on purpose
rope ladder (goes with class 1 is a bike path)
use equipment for aid

Hal Murray editorializes:
I'm an old fart. I started climbing when everybody still used pitons(metal spike with a hole through which a rope is threaded (used in mountain climbing) ). Back then, class 6 meant pitons were used for aid, class 5 meant pitons were used for protection, and class 4 meant you didn't need them but you still used a rope. But you could use trees or horns and still claim it was 4th class, so sometimes class 4 routes were pretty difficult - another branch of the game. Another description is that on a class 4 route, there is usually somebody in the group who is happy to lead everything without placing protection.
The "I would die if I fell" approach never made sense to me. I've done a lot of climbing that I call exposed 3rd where I surely would die if I fell off, but it was actually pretty easy because the holds were good and the rock was solid. Maybe I was just feeling good that day. Warm sun and a gentle breeze helps a lot.

Steve Eckert editorializes:
The problem is that class 4 and class 5 are not different except in the degree to which the route scares people. You use a rope for both, you set protection for both, and most people think you need a dynamic climbing rope for both. Class 4 is basically 5.0, and Class 5 goes all the way up to 5.13. In fact, the distinction between class 3 and class 4 is hard to draw uniformly because it's mostly based on whether people think they need a belay or not (which includes how loose or how exposed or just basically how scary it seems). This decision may change with experience, and formerly class 4 routes may become class 3!
Trying to lump everything (size of holds, looseness of rock, exposure) into a single axis is, IMHO(In My Humble Opinion if you ask me, my opinion is (Internet Slang) ),not optimal. The Yosemite Decimal system excels at differentiating how hard various technical climbs are, but it often fails to accurately describe mountaineering climbs. If you take away the handrail on an outside stairway, it is fatally exposed but still only class 1 in either system. As you narrow the width of the stairs, at some point a rope is required for safety but you still don't need your hands.

Andy W editorializes:
The rating system varies with each climbers perception of climbing, based on their own personal abilities. What one climber thinks as being "hands required", may be "done with a stroller and inline skates" by another. Attitude certainly affects rating. From what I understand, 5.10 used to be 6.0. That is, a route that could only be done as "aided", became "technical" as improvements in equipment and technique evolved.

James Schaffner editorializes:
I don't think the original question was concerned with the difference between 5.9 and 5.10, but rather the difference between hiking/scrambling/climbing classifications of all number grades. IMO, I believe it is quite subjective. As one can see from the discussions here, everyone seems to have an opinion. Even guide and instruction books can't seem to agree (even among different editions of the same book). The business about exposure(the state of being exposed to harm or risk) probably has little to do with the rating, as it appears we're talking difficulty, not risk of injury with a fall. As they say, you can drown as easily in 8 inches of water as in 8 feet, and you can kill yourself hitting your head on a rock if you fall down on a trail as easily as if you fall 1000 feet off a big wall. (Assuming you're as clumsy as I am and would actually fall down on a trail.)

Eric Beck quotes Joe Kelsey, author of the Wind River guidebook:
"I'm not sure I can explain the difference between class 2 and class 3, but I know which peaks my dogs have climbed." RJ Secor quips:
Class 1: you fall, you're stupid.
Class 2: you fall, you break your arm.
Class 3: you fall, you break your leg.
Class 4: you fall, you are almost dead (i.e., you can't breath and move your arms, legs, and head).
Class 5: you fall, you are dead.
Quoting Tom Patey: "A solo climber: a man who falls alone. A roped team: climbers who fall together."

Subdivisions of class five climbingIn Mountaineering, Freedom of the Hills, author Ed Peters explains the subdivisions of class 5:
"The experienced climber, having accomplished or attempted free climbs of varying degrees of difficulty in the YDS class 5 range, gains an understanding of the level of difficulty involved. To the beginner, however, these ratings are simply a set of numbers, understandably, easy if rated 5.0 and impossible if rated 5.13. To provide a slightly better understanding within the class for the beginner the following tongue-in-cheek description is provided:
5.0 to 5.4
There are two hand- and two footholds for every move; the holds become progressively smaller as the number increases.
5.5 to 5.6
The two hand- and two footholds are there, obvious to the experienced, but not necessarily so to the beginner.
5.7
The move is missing one hand- or foothold.
5.8
The move is missing two holds of the four, or missing only one but is very strenuous.
5.9
The move has only one reasonable hold which may be for either a foot or a hand.
5.10
No hand- or footholds. The choices are to pretend a hold is there, pray a lot, or go home.
5.11
After thorough inspection you conclude this move is obviously impossible; however, occasionally someone actually accomplishes it. Since there is nothing for a handhold, grab it with both hands.
5.12
The surface is as smooth as glass and vertical. No one has really ever made this move, although a few claim they have.
5.13
This is identical to 5.12 except it is located under overhanging rock."
Ratings are established on lead; the follower has a somewhat easier climb.

Don't believe every climbing rating

In Mountaineering, Freedom of the Hills, author Ed Peters warns against putting too much faith in published ratings:
It can sometimes be helpful to know who rated the climb; since ratings are give by humans and not by computers, human frailties can be interjected into the system. For example, some climbers will intentionally underrate climbs so that those who follow later will be impressed. Fortunately most climbers do attempt to give accurate ratings, and by the time a route is in a guide book, enough people have made the climb to show the rating as a concensus of opinion. Also remember that ratings are given for ideal conditions; unfavorable conditions can cause considerable change in a climb's difficulty.