Armour Class (AC) Conversion Between OSR/D&D Systems

In this table, you will find the AC values ​​of different editions of Dungeons & Dragons and the most important retroclones/OSR games.

B/X D&D = Dungeons & Dragons Basic/Expert sets. AD&D = Advanced Dungeons & Dragons. BFRPG = Basic Fantasy RPG. S&W = Swords & Wizardry*. BXE = B/X Essentials (name changed to Old-School Essentials). LL = Labyrinth Lord. AS&SH = Astonishing Swordsmen & Sorcerers of Hyperborea. OSRIC = Old School Reference and Index Compilation. DCC = Dungeon Crawl Classics. 1E = Advanced Dungeons & Dragons First Edition. 5E = D&D Fifth Edition. LotFP = Lamentations of the Flame Princess**.

*S&W uses both the descending and ascending systems. In the ascending system, the base AC is 10, and continues identically to DCC, although the armour types are more similar to 1E.

**LotFP has an AC of 18 as the maximum value. This value can increase if you use plate mail with a shield, you have a high dexterity or get circumstantial bonuses.

BFRPG B/X D&D,
S&W
LL,
AS&SH, BXE
1E,
OSRIC
DCC, 5E, S&W LotFP
11
(no armor)
9
(no armor)
9
(no armor)
10
(no armor)
10
(no armor)
12
(no armor)
12
(shield)
8
(shield)
8
(padded leather)
9
(shield)
11
(shield, padded)
13
(shield)
13
(leather armor)
7
(leather armor)
7
(studded leather)
8
(leather, padded)
12
(leather armor)
14
(leather armor)
14 6
(scale mail)
6
(scale mail)
7
(studded, ring)
13
(studded, hide)
15
15
(chain mail)
5
(chain mail)
5
(chain mail)
6
(scale mail)
14
(scale mail)
16
(chain mail)
16 4
(banded mail)
4
(banded mail)
5
(chain mail)
15
(chainmail)
17
17
(plate mail)
3
(plate mail)
3
(plate mail)
4
(banded armor)
16
(banded mail)
18
(plate armor)
18 2 2 3
(plate mail))
17
(half-plate)
18
19 1 1 2
(field plate)
18
(full plate)
18
20 0
(suit armor)
0 1
(full plate)
19 etc.
21 -1 -1 0 20
22 -2 -2 -1 21
23 -3 -3 -2 22
24 -4 -4 -3 23
25 -5 -5 -4 24
26 -6 -6 -5 25

Compatibility between most OSR games, and retro-compatibility with classic D&D editions, are two of their biggest attractions. If you don’t have a manual, you can use the adventures published for it with another system; conversion is easy and in most cases it can be done without prior preparation.