---
tag: 0DTXBQPA2S
kind: concept
name: Index of a subgroup
msc: [20A05]
sources:
  - url: https://en.wikipedia.org/wiki/Index_of_a_subgroup
    locator: lead section
same_as:
  wikidata: Q1464168
  wikipedia: Index of a subgroup
---

## Summary

The index of a subgroup $H$ in a group $G$ is the number of left cosets of $H$ in $G$.
For finite groups, it is $|G| / |H|$.