Document Summary: This document describes the Unreal Unit of measure and the common scale factors used.
Document Changelog: Created; maintained over time.
The current Unreal Unit scale has been determined by tweaking of many of the constants in Unreal Engine 3. As a result, deviating from this scale by a factor of 2 should be fairly straightforward, but deviating by a factor of 10 might have some subtle and hard to track down side effects. In general, Epic does not recommend changing the Unreal Unit scale by more than a factor of 2.
Current Game Scales
In all of the Unreal Tournament games, 1 Unreal Unit is equal to 2 cm.
In Gears of War approximately 2 Unreal Units equal 1 inch, because the characters are 156 units tall and a floor of a building is 256 units tall. This was decided on for grid purposes and so our cover height worked out well.
The values for gravity were not based on reality, but on what felt right.
Most licensees use a scale of 1 Unreal Unit to 1 cm.
For details on how to change the Unreal Unit scale, see the Changing Units page.