How to grade route sections: AI, WI, M, A/C and UIAA

The core principle is simple: a section grade should describe the technique required to climb it, not the overall seriousness of the route. The UIAA states explicitly that difficulty should be tied to the rock or move itself in optimal conditions, while things like exposure, poor protection, objective hazards, route-finding, retreat, rope length, overall altitude and time should be noted separately. This matters especially on ice routes, where overall and technical grades have historically coexisted and must not be conflated.

From this comes a working rule for describing a route you have already climbed:

  • grade the specific obligatory move in its own type of terrain;
  • do not bump the grade up because of the approach, descent, altitude, bivy, pack weight or general fatigue;
  • push atypical conditions into a comment: "thin ice", "wet rock", "poor protection", "loose rock", "dry mixed".

The UIAA also stresses both the inevitable subjectivity of such grades and the way local familiarity with the terrain often distorts the perceived difficulty.

What follows is a practical guide aimed specifically at grading sections, so the parameters of length and overall seriousness have been intentionally stripped out of the descriptions. Where the original scales historically include some of those parameters, only their technical core has been kept and this is called out explicitly.

1. Alpine / glacier ice — AI

There is an important caveat with AI: it is not everywhere a strictly separate, fully unified scale. The UIAA notes that WI stands for water ice and AI for alpine / permanent ice, i.e. classic permanent ice. In practical topos AI is often read through the same technical logic as the Canadian water-ice scale, but on denser and usually more predictable permanent ice. The AAC notes that AI of a given number often feels slightly easier than WI of the same number.

The AI scale

  • AI1. Ice up to roughly 50–60°, with no real technical problem. Basic crampon and tool work is required, but the key difficulty is still confidence on the terrain rather than technique itself.
  • AI2. Around 60–70°: full-on steep ice climbing, but the moves read clearly, tool placements are usually obvious and protection options are good.
  • AI3. About 70–80°: this is genuinely steep ice that demands confident front-pointing, decent economy of effort and careful tool work; good ice and reasonable spots for protection are still typically available.
  • AI4. Roughly 75–85°, with short vertical sections in places: solid technique is needed, two-tool work must be confident, and the climber should be able to move through the section without "searching" for basic moves.
  • AI5. Near-vertical ice, 85–90°: technique must already be solid, since errors in tool or foot placements quickly stack up fatigue and comfortable rest positions are scarce.
  • AI6. Very steep and genuinely demanding alpine ice: requires near-flawless technique, precision with the tools and the ability to keep climbing when the ice quality, protection or anchor reliability are no longer obvious.
  • AI7. Exceptionally hard permanent ice: very steep, very demanding both technically and mentally; this is no longer "just a steeper AI6" but a zone where the slightest inefficiency immediately becomes a problem.

2. Water ice — WI

WI is a scale for seasonal water ice. Unlike a pure slope angle, it has historically taken into account not just steepness but also how comfortable it is to move, rest and place ice screws, meaning two lines at the same angle can carry different WI grades. This is exactly why, when describing a WI section, what matters is not the meters but the character of the ice: monolithic or brittle, presence of ledges, whether screws go in cleanly, whether the column is hanging, whether the surface crust shears off.

The WI scale

  • WI1. Low-angle ice that is more walked than "climbed".
  • WI2. Stable sections around 60°, with possible small bulges, but technique and protection are usually straightforward.
  • WI3. About 70° with possible steep bulges to 80–90°; a confident rhythm is required, but reasonable spots for rests and ice-screw placements still exist.
  • WI4. Sustained steep ice around 80°, or significant vertical sections separated by occasional rests; technique must be solid and economy of motion already matters.
  • WI5. Near-vertical ice at 85–90° with few good rests, or thinner / poorer-quality ice where a screw is hard to place.
  • WI6. Almost continuous vertical, or an even thinner and more nervy version of WI5: high technical demands, an unforgiving ice character, and a need for precision.
  • WI7. Thin, poorly bonded or overhanging ice and columns where protection either barely goes in or is of doubtful quality; this is the edge where the very structure of the ice becomes part of the core difficulty.

3. Mixed — M

The M scale describes mixed climbing: crampons and ice tools on a combination of ice, névé, rock and dry sections. The AAC states explicitly that such routes require dry tooling in crampons and that real ice may be scarce; the UIAA adds that the letter M originally appeared to designate mixed sections and was later applied to more sport-style dry tooling as well. In other words, M is first and foremost about the technique of moving with tools and crampons through mixed terrain, not about the overall alpine seriousness of the line.

There is one nuance with the official short definitions: the AAC lumps M1–M3 into a generic "easy" range and M9–M12+ into a single high-grade block. So below is a working practical breakdown within those ranges, compatible with the spirit of the source but not claiming the status of a separate official standard.

The M scale

  • M1. Very easy mixed: tools and crampons help maintain rhythm rather than solve a real technical problem.
  • M2. Short steep mixed steps appear, but they are straightforward and do not require complex dry-tooling technique.
  • M3. Distinct mixed climbing where the tool serves not just for balance but as a proper move; no hard dry tooling yet.
  • M4. Low-angle to vertical terrain with noticeable technical tool work.
  • M5. Sustained vertical mixed moves, where dry tooling is now constant rather than occasional.
  • M6. Vertical to slightly overhanging: hard dry tooling, where errors in precision are punished quickly.
  • M7. Overhanging, powerful and technical mixed.
  • M8. Roofs appear; very powerful and very technical tool moves are required.
  • M9. Roofs and overhangs grow longer, and tool placements become less obvious.
  • M10. Long, powerful overhanging sequences with fewer "easy" solutions.
  • M11. Very sustained overhanging mixed, where pronounced power-endurance is now required.
  • M12 and above. The same logic taken to the limit: longer roofs, more powerful moves, thinner and more precise placements.

4. Aid — A and C separately

In aid climbing the number means something different than in free climbing. Here the grade reflects not only "how hard the move is" but also which placements you set, how reliable they are and what happens in a fall. The AAC explicitly distinguishes the old and New Wave readings of aid grades, and the UIAA separately records that A refers to aid climbing in general, while C refers to clean / ecological / hammerless aid, i.e. without a hammer and without damage to the rock.

A — classic aid climbing

  • A0. Occasional pulls on fixed gear, the rope or an existing placement; the minimal level of aid.
  • A1. All placements are bomber and go in without drama.
  • A2. Placements are generally good, but finding and setting them is noticeably harder.
  • A2+. Genuinely nervy placements with real fall potential appear, but without expected serious consequences.
  • A3. Many marginal or thin placements in a row; precision and patience are required, with little safety margin.
  • A3+. As A3, but with truly dangerous fall potential.
  • A4. A sequence of placements that mostly hold body-weight only; serious potential for a hard fall.
  • A4+. Even more serious than A4, both in gear quality and in the consequences of an error.
  • A5. Nothing on the section can be trusted to hold a fall.
  • A6. Same as A5, but the anchor itself may not survive a leader fall.

For the European aid tradition the UIAA emphasizes the difficulty of placements, work in aiders, passing overhangs, the use of hooks, skyhooks and rurps, and the growing precariousness at A4–A5. For grading a section this means: do not inflate the A-grade because the pitch is long; bump it up only when placements are worse, harder to set and the consequences of a fall are more serious.

C — clean aid, hammerless aid

The C scale reads the same levels through clean style: no hammer, no piton driving, only passive removable protection. The UIAA describes C0–C5 explicitly as "ecological style", i.e. without a hammer. So the difference between A and C is not "more or less hard" but how the same class of aid climbing is carried out.

  • C0. Brief, direct use of existing placements or fixed gear.
  • C1. Simple and bomber clean placements.
  • C2. Placements are reliable but harder to find and set.
  • C2+. Nervy placements with real fall potential start to appear.
  • C3. Many marginal placements; you need to understand precisely what you are placing and why.
  • C3+. As C3, but with dangerous fall potential.
  • C4. A long series of body-weight-only placements; an error can be costly.
  • C4+. Even more serious in consequences and placement quality.
  • C5. Nothing on the section can be trusted to hold a fall.

A or C

A simple rule:

  • climbed on passive removable gear without a hammer — write C;
  • used a hammer, pitons, bolts and similar gear — write A.

Pick the number based on placement quality and the cost of a mistake, not on pitch length.

5. Rock — UIAA

For rock the UIAA is a free-climbing scale, and it has always required a strict separation of free from aid. Its purpose is to grade the difficulty of specific free moves, while exposure, poor protection, objective hazards, looseness, route-finding difficulty, rope length, overall altitude and time should be described separately. The UIAA text itself stresses that this scale is particularly well-suited to classic routes, where moves of varying difficulty may be encountered within a single pitch.

The correct UIAA notation is in Roman numerals with + and -: IV+, V, VI-. The UIAA notes explicitly that Arabic numerals do not belong to this scale; if you mean UIAA, write V+, not 5+.

The UIAA scale

  • I. The easiest climbing / scrambling; hands are often used for balance.
  • II. Climbing proper begins here: movement must be deliberate, but holds and footholds are still plentiful.
  • III. Steeper rock, sometimes already vertical; holds are less frequent, and strength is needed in places.
  • IV. Holds and footholds are smaller and rarer; sound basic technique is required on arêtes, chimneys, cracks and corners.
  • V. Holds are small and sparse; climbing becomes either delicate or powerful, and reading the moves in advance is often useful.
  • VI. Small holds are arranged to demand a precise sequence of moves; on steep rock this is already a level requiring specific training and strong fingers and arms.
  • VII. Very small and widely spaced holds; advanced balance and gripping technique are required, along with high precision of movement.
  • VIII and above. The scale is open: the same logic continues, but precision, power demands and sequence complexity all increase.

Do not inflate UIAA out of fear

Bad protection — say so: UIAA V+, poor protection. Loose — UIAA IV, loose. Wet — UIAA IV+, wet. The Roman numeral itself must remain the number for free technical difficulty, otherwise the description becomes useless to the next party.

How to record combined sections

For alpine routes it is normal to use several scales at once: the UIAA itself gives an example of a combined grade for an ice line via overall, technical and special notations, and in modern descriptions it is equally normal to call out WI, AI, M, UIAA and A/C separately for different moves of the same route. If a section contains both free and aid climbing, the UIAA explicitly allows notation such as V+ obl. and A0 or 6b obl. and A1.

Practically useful formats:

  • AI4, thin ice
  • WI5, brittle ice, screws hard to place
  • M6, dry
  • UIAA V+, loose
  • A2+
  • C3
  • UIAA V+ obl. and A1

This gives the next party exactly what it needs: what they will have to climb, not a story about how hard the whole route felt to you.

In summary

A good description of a climbed section almost always consists of two layers:

  1. Pure technical grade in its own scale.
  2. Short notes on conditions and seriousness.

Matching scale to terrain:

  • rock — UIAA;
  • glacier ice — AI;
  • water ice — WI;
  • mixed terrain — M;
  • aid climbing — A or C.

The more strictly you separate technique from length, danger and context, the more useful your description becomes to other climbers.

Sources

  1. UIAA. The Scales of Difficulty in Climbing ↗.
  2. AAC. International Grade Comparison Chart ↗.
  3. AAC. The UIAA Climbing Classification System ↗.