Illustrations of history

"war horse" is a broad term. If you meant "horses rode into battle", then afaik they were generally pretty small, since smaller horses are more maneuverable and accelerate better. They probably also need less armor, etc.

Horses used in war, but not in battle could be bigger, especially packhorses.

They also mostly classed horses by use, not by breed. We don't really know what breed a "charger" is, unless it's from genetic samples, or the rare artist who actually drew horses correctly.