Other People’s Posts – Crit Hit Range based on Armor worn (D&D)

Castles and Chimeras is an OSR Blog I stumbled across when it went live with a simple but great concept idea:

Critical Hit Range is based on the armor worn by the defender.

In short, I love it. I might tweak a bit, because some monsters may have good armor class but wear no armor due to natural protection such as plates and scales and thick hide.

So it wouldn’t be crazy to make a simple guide converting AC to a critical range.

He pegs “unarmored” as a crit on 15 through 20. That range is 5 wider than the usual 20-only.

D&D5 pegs bonuses to AC from +0 for nekkid to +8 for Plate. 

So take half the armor bonus, divide that number by 2, and subtract it from 4. That’s the additional critical hit range you get. Note that the table below assumes you’re wearing a helmet and nothing else. If you aren’t wearing a helmet, add 1 to the crit range. 

So, that would give you

This has the nice effect that weaker armor makes you much more likely to receive a severe blow. Note that this does not include the DEX bonus. It’s the armor only. This makes an armor with an AC bonus of 4 better in some respects than armor with a DEX bonus of +4 due to the character but an Armor Bonus of +1, even though they’re equally as likely to get hit.