Rock climbing comes in many forms; there are short, sport climbs on roadside crags equipped with bomb-proof bolts for protection, very long and adventurous alpine rock climbs, and just about everything in between. Given this varsity of climbing, different character of different climbing areas and different historical background and climbing ethics, it is hardly a big surprise that there are numerous different systems to grade rock climbing routes.
Climber who makes the first ascent (leading, of course) grades the climb as he or she sees fit. Other routes on the same area are logical benchmarks for new routes. This can lead to rather systematic differences between areas, with some having the reputation of every climb feeling harder than similarly graded climbs elsewhere.
As the route is climbed, it's grade may change because of several reasons. If the route is initially overrated, the grade may be lowered. However if the route is underrated (sandbagged), it almost never gets new rating. Also breaking of the rock, corrosion etc. may cause the difficulty of a certain route to change. These changes, however, seldom have any impact on the grade.
If a climber is unfamiliar with specific type of rock and techniques well-suited for the type of climbing (crack climbing, for example), a route can feel much harder than similarly graded climb of other character. Also physical attributes of climber (height for instance), can have significant impact of subjective feeling of the difficulty.
Even if the grading system is very same, some routes can feel much easier or harder than other similarly graded routes. This is due the subjective nature of climbing grades. There are numerous reasons for variations, some of which are discussed in the following.
Many grading systems (such as UIAA, French and Yosemite Decimal Systems) are primarily (or entirely) concerned about the most difficult move (for multipitch routes, sometimes each pitch is graded separately). Thus all other factors, such as length, difficulty and reliability of protection, how sustained the difficulties are, length of approach, ease of descent etc. are either totally omitted or get very little weight when deciding the grade. The system used to grade trad climbs on British Islands is a notable exception. There are, however, other exceptions and differences, so converting grades from system to another is not straightforward.
Most systems give redpoint grade (that is to say that grades assume the climber to be familiar with the route). Thus it is quite possible that two routes graded identically may feel totally different when climbing them onsight. British trad system is, once again, notable exception, as it gives onsight grades (assuming climber has no prior knowledge of the route).
Since most grading systems only concern technical difficulty of the most difficult move or section, the systems work well for comparing sport climbs. With trad routes in general, and alpine routes in particular, significant part of the difficulties are psychological in nature. It is one thing to lead a grade 6 climb on a crag equipped with bomb-proof bolts some three meters apart, climbing at the similar technical standard on poor rock some 10 meters above the last protection is another. On long trad routes route finding, difficulty of retreat, objective hazards and sheer scale of the undertaking make climbing feel more committing and often more difficult than mere technical difficult would suggest.
There are many ways to remedy this shortcoming. First of all, some systems don't deal with this issue at all. In some cases this may not be necessary, anyway, as the if the route is alpine in nature, the overall alpine grade is often used. This, however, does not cater for non-alpine climbs, that are particularly seriousness. The other way to add notion to grade, when the route is particularly dangerous. More complete solution is the British trad grade and e-grade system.
Especially when visiting foreign areas, choosing suitable trad route for onsighting can be very difficult. Granted, adventure and surprises are part of the attraction of trad climbing, but inability to judge whether a route is safe to try can literally be a matter of life and death. Therefore some system to communicate the protectability of a trad route makes sense.
As far as I know there are several approaches that could theoretically be used to include seriousness in the grade:
I personally hate the first approach, as it tries to combine two very different into a single figure, thus making it impossible to know whether we are talking about climb that's easy for the grade with bad gear, normally protectable climb or route that's hard for the grade but on excellent gear.
Either of the other two approaches can be great. Grade that depends on the route difficulty may give more precise information, but is more complicated and far more subject to subjective interpretation, therefore I believe that it is probably better to stick with the system that does relate technical difficulty and seriousness/protection.
UIAA grades are mostly used for routes found in alpine settings. They are, however, used in Austria and parts of Germany to gared also routes of non-alpine character. Grades are based on redpoint ascents (prior knowledge of the route assumed). The scale is open-ended and "+" and "-" are used to refine grades. There are many other grading systems (such as Swedish and Norwegian) that are derived from UIAA system, although the meaning of grades may be significantly different from original UIAA scale.
French system is also used in Spain and Italy and is increasingly popular to grade sport climbs in other areas as well (particularly for high-level routes). The system aims to tell how hard it is to redpoint a route with complete information about the route. Grade tries to indicate difficulty of a whole pitch, thus it gives no information whether the route is sustained with slightly lesser difficulties or has a difficult crux and is generally easier. Grade expects the climber to be familiar with the route, thus onsighting two different routes with the same French grade may be radically different.
Yosemite Decimal system uses classes to indicate the type of terrain. Class 1 stands for hiking and actual rock climbing is class 5. Sometimes class 6 is used to refer to aid climbing. Class 5 is further divided in open-ended decimal system. Grades from 5.10 upwards are subdivided into categories a, b, c and to refine the grading. The system rates solely the hardest move of a pitch (hardest move of the hardest pitch for multipitch climbs). However, very sustained 5.9 pitch may be graded 5.10(a). Grades are redpoint grades (full knowledge of the route assumed).
The system was closed-ended until 1960's running from 5.0 to 5.9. Not all routes of that era are re-graded, so old 5.9 climbs may actually be harder.
Since Yosemite decimal system does not consider the seriousness of a route, it is possible that that letter suffix is used to indicate the protectability/seriousness. The principle is simple enough:
In practice, the usage of such letters vary greatly between different areas and often only R and X are used. However, the lack of them is by no means indication of safely protectable route.
The system used to grade trad climbs on British Islands is in many aspects quite different from most other systems. First of all, it gives onsight grades, as opposed to most other system's redpoint grades (many of the bold routes are redpointed, though). Also, British system consists of two parts:
The interaction of both parts give information about the character of a route. The routes with high adjective grades and low technical grades will generally be poorly protected (such as HVS 4b, E1 4c, E2 5a) whilst those with low adjective grades and high technical grades will be relatively safe (i.e. HVS 5c, E1 6a, E2 6b ). Routes falling between these two scenarios will most likely have a bit of both. This is only a general indication though since routes can also be bold within the parmeters indicated above.
The German grading system considers the seriousness or Ernsthaftigkeitsgrad of a climb. This grading scale considers all aspects of the climb which have nothing to do with the technical difficulty: average runout distance, quality of the protection placements, objective dangers, quality of the rock, etc. The scale goes from E0 to E5. E0 is a normal route, with solid fixed pro and ample opportunities for placing pro. E5, at the other end of the scale, stands for a largely unprotected and unprotectable route with manky pitons and crummy rock. On an E5 climb, falling is generally a lethal idea. In most topos, routes with an Ernsthaftigkeitsgrad above E0 are marked as such.
On parts of the Eastern Alps, especially Southern-Tirol and Dolomites, e-grade (Ernsthaftigkeitsgrad) is used together with conventional rock grade. It's aim is to give information about overall seriousness and psychical demands of a route. It considers the following factors in that order:
The e-grade is always given in relation to grade of technical difficulty. If the most difficult sections can be aided, separate grade for that may also be used. Thus the whole cotation is for example 7-/e VI-/V+ A0 (Comici on Cima Grande, alpine grade ED-, 500m), meaning it's 7- if redpointed (all free), is well protected (thus e-grade is a whole grade lower than the technical grade) and it is V+ if the crux is aided (A0, pulling on the fixed gear). A route of similar technical standard, where the protection would be considered normal for a climb graded 7- would be 7-/e VII- and badly protectable climb of similar technical difficulty is something like 7-/e VIII. The e-rade is always given in relation to technical difficulty of a route and may differ up to +/- grades from the technical grade.
Traditionally, a system derived from UIAA grade has been used to grade both trad and sport climbs. Finnish grade's have been roughly a full grade stiffer than the UIAA grades. For particularly dangerous routes, sometimes letter V has been added as a suffix.
In the most recent guidebook sport climbs have been graded with french grade, which had been widely used to grade the most difficult routes anyway.
Also in recent years, topos of trad areas on SW Finland introduced their own version of E-grade to indicate the protectability of a route. The scale runs from 1 to 5, but instead of the numbers the topos use animal symbols ranging from Bear (well protected) to spider (barely protected).
There is a number of grading system used for boulders. These are not discussed here. However, links to resources covering them are included in the links section of this document.
"It's always further than it looks. It's always taller than it looks. And it's always harder than it looks."
- The 3 rules of mountaineering
The following table tries to make comparing grades of different systems easier. The alpine grading system is put here for a rough reference only.