Boots and crampons: the compatibility rules

A crampon is a frame of spikes strapped or clipped to a boot, and it only works if the boot underneath does not bend independently of it. A flexible boot flexes at every step; a rigid crampon attached to it either works loose or is levered off, and both of those happen at the worst moment rather than in the car park.

So boots are rated for how much they flex and crampons for how much flex they tolerate, and the two ratings are designed to be read together. This is the whole of the system, and once the reason is clear the letters stop being arbitrary.

The rating scheme in common use, and what each level is for:

B0 boots

Flexible walking bootsNo crampon compatibility. Flexible sole, no attachment points.

B1 boots

Stiffened walking bootsSome sole stiffness, for general winter walking. Takes a C1 crampon.

B2 boots

Mountaineering bootsStiffer, usually with a heel welt for a clip. Takes C1 or C2.

B3 boots

Fully rigid technical bootsWelts at heel and toe. Takes any crampon including fully step-in C3.

C1 crampons

Flexible, strap-onWalking crampons. Go on almost anything from B1 upward.

C2 crampons

Semi-rigid, heel clipNeed a heel welt, so B2 or B3. General mountaineering.

C3 crampons

Rigid, step-in both endsNeed welts at both ends, so B3 only. Technical ice.

The rule that follows is short: the crampon number must not exceed the boot number. A C1 goes on a B1, B2 or B3. A C2 needs at least a B2. A C3 needs a B3. Going the other way does not work and is not a matter of being careful.

The scheme is a convention rather than a standard with a single custodian, and it is not applied identically by every manufacturer. Some boots are marked with it and some are not, some sit between two ratings, and boot shapes vary enough that a crampon rated correctly can still fit a particular boot badly.

Which is why the letters are a filter rather than an answer. The actual test is fitting the crampon to the boot you own, adjusting it, and checking it holds — and any shop selling both will do this with you. Buying the two separately online, from different sellers, on the strength of matching letters, is the specific way this goes wrong.

Boots first, always, and fitted in person. They are the item where fit dominates specification, they are the item you cannot hire satisfactorily, and they determine what crampons you can ever use. For somebody moving into winter walking, a B1 or B2 boot covers everything they will do for several years.

Crampons second, and after a course rather than before it, when you know what you are doing with them. C1 or C2 covers general winter mountaineering and nearly nobody outside technical ice climbing needs a C3. Buying used is reasonable for crampons — they are hard goods, damage is visible, and points can be sharpened — and much less reasonable for boots, where the previous owner’s feet have already shaped them.