Version 0.19: This article may not be up to date for the latest stable release of Crawl.
The Armour skill improves the effectiveness of your armour and reduces most of the penalties associated with the more cumbersome varieties of body armour.
If you're interested in the actual math the game uses, see the AC calculations page. Otherwise, the short version is that each level in the Armour skill increases the base AC of a piece of armour by a little over 4%. The Armour skill also partially defrays your armour's encumbrance rating, making it easier to evade attacks or cast spells. However, no amount of Armour skill will reduce the stealth penalties of armour.
Felids, Draconians and Octopodes cannot train Armour due to their body restrictions.
|Weapons|| Short Blades • Long Blades • Ranged Weapons
Axes • Maces & Flails • Polearms • Staves • Unarmed Combat • Throwing
|Physical||Fighting • Armour • Dodging • Stealth • Shields|
|Magical||Spellcasting • Invocations • Evocations|
|Spell Schools||Air • Conjurations • Earth • Fire • Hexes • Ice • Necromancy • Poison • Summoning • Translocations • Transmutations|