HipHeight determines the distance (in studs) off the ground the Humanoid/RootPart should be when the Humanoid is standing. The Humanoid/RigType|RigType influences the way this property behaves:

HipHeight for R15 Humanoids

With R15 rigs, a suitable HipHeight is preset to ensure the height of the Humanoid/RootPart is correct. The height of the legs is not used. The overall height of the Humanoid can be described in the following formula:

Height = (0.5 * RootPart.Size.Y) + HipHeight

HipHeight for R6 Humanoids

For R6 rigs, the Humanoid/RootPart|RootPart's height is determined by the height of the character’s legs and Humanoid/RootPart. HipHeight instead describes a relative offset. The overall height of the Humanoid can be described in the following formula:

Height = LeftLeg.Size.Y + (0.5 * RootPart.Size.Y) + HipHeight