Unlike grading systems of other types of climbing, the same system is used to grade all aid climbs (which is not to say that all techno routes featuring same grade would be equally hard). Aid climbing grades indicates mainly the difficulty and quality of protection placements. Minor (upward) changes in difficulty can be marked with +-sign. Aid climbing grade are subject to change because of developing equipment and wear of the rock. For climbs, where no destructive means of protection (most notably pitons) is used, "A" is replaced with "C" (as in clean).

A0Fixed pieces of protection are already in place. Possibly A0 climb can involve the climber placing slings to climb some passages. Few classic alpine ascents have fixed gear that make the routes significantly easier than they would be without the gear. Such routes include Matterhorn, Hörnligrat (AD-, III and A0) and Dent du Géant, Normal Route (SW Face, AD, III, A0).
A1Pitons, hooks, wedges etc. are relatively easy to put in place. Does not yet require much force and virtually every placement is perfectly capable of holding a fall. The use of full aid technique and gear (such as ladders) are not always necessary. A1 climbs often get climbed "French free", meaning that the climber uses protection to aid progress by simply grabbing them.
A2Protection placements are fairly good, but placing the pieces may not be without difficulties. Between good placements there may be some less perfect placements.
A3A3 is hard aid. Normally leading a pitch takes several hours and there are potentially falls of 20-25 meters length, but without danger of grounding or severe injury. Active testing of soundness of placement is required.
A4Serious aid. Fall potential up to 35 meters with bad landings. Placements hold only body weight.
A5Placements hold only body weight for entire pitch with no solid protection. A leader fall at the top of an A5 pitch means a 100 meter fall with possibly lethal consequences.
"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