In the area of abstract algebra known as group theory, the diameter of a finite group is a measure of its complexity.

Consider a finite group ${\displaystyle \left(G,\circ \right)}$, and any set of generators S. Define ${\displaystyle D_{S))$ to be the graph diameter of the Cayley graph ${\displaystyle \Lambda =\left(G,S\right)}$. Then the diameter of ${\displaystyle \left(G,\circ \right)}$ is the largest value of ${\displaystyle D_{S))$ taken over all generating sets S.

For instance, every finite cyclic group of order s, the Cayley graph for a generating set with one generator is an s-vertex cycle graph. The diameter of this graph, and of the group, is ${\displaystyle \lfloor s/2\rfloor }$.^[1]

It is conjectured, for all non-abelian finite simple groups G, that^[2]

${\displaystyle \operatorname {diam} (G)\leqslant \left(\log |G|\right)^((\mathcal {O))(1)}.}$

Many partial results are known but the full conjecture remains open.^[3]