I have been wondering what type of measurement is used to measure the space inside of a four dimensional (space, not time) object. For example, a one dimensional line's distance gets measured, a two dimensional object's area gets measured, and a three dimensional object's volume gets measured, but what type of unit do four dimensional objects get? I am not looking for a specific measurement, such as inches, liters, or square centimeters. What is the category that four dimensional measurements fall under? I have looked all over the internet, but could not find an answer, so I decided Physics Forums looked like a good place to ask.