AC calculations

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Version 0.14: This article may not be up to date for the latest stable release of Crawl.


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 + Beogh 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. If you're a follower of Beogh, you receive an additional bonus, increasing with Piety. This additional bonus maxes out at +10 when you reach 160 Piety.

A follower of Beogh with max Piety and 27 Armour skill has the AC of all armour pieces increased to roughly 245% 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: