D&D Critical Hit Calculator

How to Use the Critical Hit Calculator

1. Enter your weapon damage dice, such as 1d8 for a longsword or 2d6 for a greatsword.
2. Add your static damage modifier (usually Strength or Dexterity plus magic weapon bonus).
3. Specify extra dice like sneak attack (d6) or divine smite (d8) by entering the number of dice rolled.
4. Press Roll Damage. The calculator rolls once for a normal hit and again with doubled dice for a critical hit, keeping modifiers applied once.
5. Review the breakdowns to see exactly which dice contributed to the total. Recent rolls stay in the history for quick reference.

Features for Martial Classes

• Weapon Dice Control: Input any combination of dice to model versatile weapons or extra attack features.
• Bonus Dice Options: Sneak attack, divine smite, and a custom extra dice slot cover most class features.
• Normal vs Critical: View both results side-by-side to evaluate the impact of features like Improved Critical.
• History Log: Track up to six rolls to average expected crit damage across encounters.
• Transparent Dice: The breakdown shows every individual die, so your DM can see the actual results.

Critical Hit Rules in D&D 5e

In 5th Edition, a natural 20 on an attack roll is a critical hit. All damage dice for the attack are rolled twice, including weapon dice, smite dice, sneak attack dice, and any other damage dice from class features or spells. Static modifiers such as ability bonuses or magic weapon bonuses are added once. Some abilities expand the critical range (Champion Fighters crit on 19-20), while others add additional dice when a crit occurs (Brutal Critical, Savage Attacker).

Divine Smite and Sneak Attack dice are doubled because they are damage dice. However, riders that deal fixed damage (like Hex’s 1d6 per hit) also double. Features that add flat bonuses (Hexblade’s Curse + proficiency) do not double. House rules sometimes set crit damage to “max damage + normal roll,” but this calculator follows the official RAW approach.

Examples and Tips

A level 9 rogue rolling a rapier attack would enter 1d8 weapon dice, +4 modifier, and 5d6 sneak attack dice. When a crit lands, the tool doubles both the weapon and sneak dice, instantly showing the burst potential. Paladins can enter their smite dice based on slot level; a 3rd-level smite adds 4d8 that double on a crit. Combine this calculator with the attack roller, saving throw roller, and fireball calculator to manage every combat scenario without guesswork.