AC calculations
This page explains how the game calculates and uses AC.
Calculating AC from Armour
The formula for calculating the actual AC granted by wearing a piece of armour is as follows:
(base AC) * (22 + Armour skill + Racial armour bonus/2) / 22
This means that every level in the Armour skill increases a piece of armour's AC by approximately 4.5% of its base AC. As for racial armour bonuses, they effectively act as bonus levels in the Armour skill. They are as follows:
- Dwarven armour grants all species a +4 bonus (roughly +9% to base AC). Deep dwarves receive an additional +4 for a total of +8 (roughly +18% to base AC).
- Elven armour grants high elves and deep elves a +2 bonus (roughly +4.5% base AC).
- Orcish armour grants Hill Orcs a +4 bonus (+9% base AC). If you're a follower of Beogh, you receive an additional bonus, increasing with Piety. This additional bonus maxes out at +9 when you reach 180 Piety, for a total of +13 (roughly +29% to base AC).
A hill orc follower of Beogh with max Piety and 27 Armour skill has the AC of all orcish armour pieces increased to roughly 252% of their base value.
Note that fractional AC from multiple pieces of armour does add! Fractions are not truncated until the contribution from all armour pieces are summed. For example, both a helmet and a pair of gloves have 1 base AC, so at an Armour skill of 12 they each provide 1.55 AC, which is rounded down to 1 AC when worn individually. When worn together, their contributions sum to 3.1 AC, which is rounded down to 3 AC.
Other Sources of AC
All other sources of AC are applied directly to a character's total AC and are not modified by Armour skill whatsoever. These include:
- Bonus AC from enchanted armour, rings of protection, or artefacts
- Magical AC boosts such as Ozocubu's Armour or Stoneskin
- AC from transmutations such as Necromutation, Statue Form and Dragon Form
- AC from mutations (e.g. scales) and intrinsics (e.g. a naga's increasingly tougher skin)
