Hit Dice by Size

Monster Size Hit Die Average HP per Die
Tiny d4 2 1/2
Small d6 3 1/2
Medium d8 4 1/2
Large d10 5 1/2
Huge d12 6 1/2
Gargantuan d20 10 1/2

A monster's Constitution modifier also affects the number of hit points it has. Its Constitution modifier is multiplied by the number of Hit Dice it possesses, and the result is added to its hit points. For example, if a monster has a Constitution of 12 (+1 modifier) and 2d8 Hit Dice, it has 2d8 + 2 hit points (average 11).

This work includes material taken from the System Reference Document 5.1 ("SRD 5.1") by Wizards of the Coast LLC and available at https://dnd.wizards.com/resources/systems-reference-document. The SRD 5.1 is licensed under the Creative Commons Attribution 4.0 International License available at https://creativecommons.org/licenses/by/4.0/legalcode.