Mostly Harmless
Legacy:Unreal Unit
UU stands for Unreal Units. Any number that represents a distance in Unreal is given in these units. There's also RUU, Rotational Unreal Unit (or Unreal Rotation Unit, but it's easier to link RUU than URU ;) ). Often "UU" is used for both length and angle, and sometimes they are just called "units", or not given a name at all ("build a 256x256x64 box").
Length[edit]
The UnrealEd grid, dimensions of brushes, positions of actors and sizes of collision cylinders are all measured in these units. The Unreal World can have a maximum size of 65536 UU (=2^16) in Unreal/UT. UT2003 and U2 have worlds of 524288 UU (=2^19).
One UU doesn't actually mean anything, it's just something within the engine. An arbitrary scale is used for game programming because the scale may change from one game to another, one game may be an FPS, while another may be a space sim with several planets on an entire map. Each game picks a scale to work at: the size of players and objects, which means there is an effective conversion factor between UU and real physical units. In the Unreal series of games, this is generally held to be roughly:
 256 UU = 487.68 cm = 16 feet.
 1 meter = 52.5 UU
 1 foot = 16 UU
 1 cm = 0.525 UU
 1 UU = 0.75 inches
Sweavo: in ut2004, a 52.5 square space is just enough for a player to fit in. I would increase all these numbers by 20% if making semirealistic maps.
Angle[edit]
Some UnrealScript functions use radians, just to be awkward, or because they're always used with radians, such as trigonometric functions.
Unreal Units  Degrees  Radians * π  Steps per circle 
1024  5.625  1/32  64 (default step size of the rotation grid) 
2730  15  1/12  24 (not quite round, it's actually 2730.6666... ) 
8192  45  1/4  8 
16384  90  1/2  4 
24576  135  3/4  2.66... 
32768  180  1  2 
65536  360  2  1  full circle 
See also the rotation grid in UnrealEd Advanced Options>Editor>RotationGrid, set:
Angle conversion constants[edit]
const DegreeToMOA = 60.0; // 21600/360 const DegreeToRadian = 0.017453; // pi/180 const DegreeToURot = 182.044449; // 65536/360 const MOAToDegree = 0.016667; // 360/21600 const MOAToRadian = 0.000291; // pi/10800 const MOAToURot = 3.034074; // 65536/21600 const RadianToDegree = 57.295776; // 180/pi const RadianToMOA = 3437.746582; // 10800/pi const RadianToURot = 10430.377930; // 32768/pi const URotToDegree = 0.005493; // 360/65536 const URotToMOA = 0.329590; // 21600/65536 const URotToRadian = 0.000096; // pi/32768
Conversion utilities[edit]
If you want to use a handy unit conversion, you can use a postoperator for this, like so:
const Meter=52.5; // These can be somewhere fairly global... static final postoperator float Meters( float Units ) { return Units * Meter; } static final postoperator float MPS( float Units ) { return Units Meters; } function SetSomething() { SetCollisionSize( 5 Meters, 3 Meters ); Velocity = Vector( Rotation ) * 5 MPS; }
See Useful Maths Functions for angle conversion factors.
Two handy javascript unit converters:

UU_Convert
(2002)
 (does anyone have updated links for this? These are dead. gblues)
 for linear units: dead link

for
angular
units:
dead
link
 Standalone version/utility: dead link
 Feature list (warning: popups): http://www.angelfire.com/games3/thealien/util_ut.html

REAL2UNREAL
(2004)

for
linear
and
angular
units:
http://streamlab.info/real2unreal/
 Standalone version/utility: http://streamlab.info/download/real2unreal0.3b.zip

for
linear
and
angular
units:
http://streamlab.info/real2unreal/