When doing replacement or upgrading on 2000 – 2018 Audi TT Quattro capsule halogen headlamps HID with, the bulb size guide is necessary for you to take the reference.
Jump to corresponding car model with the catalog bellow.

Low Beam Headlight2000 – 2006 H1
2008 – 2009 H7
High Beam Headlight2000 – 2006, 2008 – 2009 H7
Front Fog Light2000 – 2006 H3-55W
2008 – 2009 H8/H11/H16
Back Up Light2000 – 2006 1156
2008 – 2009 921
Brake2008 – 2009 1156
2000 – 2006 1157
Dome Light2000 – 2006 578
Front Side Marker2008 – 2009 12396NA
2000 – 2006 H6W
Front Turn Signal2000 – 2006, 2008 – 2009 H21W
License Plate2000 – 2006, 2008 – 2009 12844
Parking Light2008 – 2009 12396NA
2000 – 2006 H6W
Rear Side Marker2000 – 2006 12961
Rear Turn Signal2000 – 2006 1156
2008 – 2009 921
Tail Light2008 – 2009 1156
2000 – 2006 1157
Courtesy2000 – 2006, 2008 – 2009 6418
Glove Box2000 – 2006 12256
2008 – 2009 12961
Map Light2008 – 2009 12961
Trunk2000 – 2006 12961
2008 – 2009 194
Low Beam Headlight2000 – 2006 D2S
High Beam Headlight2000 – 2006 H7
High Beam and Low Beam Headlight2008 – 2009 D1S
Front Fog Light2000 – 2006 H3-55W
2008 – 2009 H8/H11/H16
Back Up Light2000 – 2006 1156
2008 – 2009 921
Brake2008 – 2009 1156
2000 – 2006 1157
Daytime Running Light2008 – 2009 1156
Dome Light2000 – 2006 6411
Front Side Marker2000 – 2006, 2008 – 2009 H6W
Front Turn Signal2000 – 2006 H21W
2008 – 2009 PY21W
License Plate2000 – 2006, 2008 – 2009 12844
Parking Light2000 – 2006, 2008 – 2009 H6W
Rear Side Marker2000 – 2006 12961
Rear Turn Signal2000 – 2006 1156
2008 – 2009 921
Tail Light2008 – 2009 1156
2000 – 2006 1157
Courtesy2000 – 2006, 2008 – 2009 6418
Glove Box2000 – 2006 12256
2008 – 2009 12961
Map Light2008 – 2009 12961
Trunk2000 – 2006 12961
2008 – 2009 194
Low Beam Headlight2000 – 2006 H1
2008 – 2012 H7
High Beam Headlight2000 – 2006, 2008 – 2012 H7
Front Fog Light2000 – 2006 H3-55W
2008 – 2012 H8/H11/H16
Back Up Light2000 – 2006 1156
2008 – 2012 921
Brake2008 – 2012 1156
2000 – 2006 1157
Dome Light2000 – 2006 578
Front Side Marker2008 – 2012 12396NA
2000 – 2006 H6W
Front Turn Signal2000 – 2006, 2008 – 2012 H21W
License Plate2000 – 2006, 2008 – 2012 12844
Parking Light2008 – 2012 12396NA
2000 – 2006 H6W
Rear Side Marker2000 – 2006 12961
Rear Turn Signal2000 – 2006 1156
2008 – 2012 921
Tail Light2008 – 2012 1156
2000 – 2006 1157
Courtesy2000 – 2006, 2008 – 2012 6418
Glove Box2000 – 2006 12256
2008 – 2012 12961
Map Light2008 – 2012 12961
Trunk2000 – 2006 12961
2008 – 2012 194
Low Beam Headlight2000 – 2006 D2S
High Beam Headlight2000 – 2006 H7
High Beam and Low Beam Headlight2008 – 2012 D1S
Front Fog Light2000 – 2006 H3-55W
2008 – 2012 H8/H11/H16
Back Up Light2000 – 2006 1156
2008 – 2012 921
Brake2008 – 2012 1156
2000 – 2006 1157
Daytime Running Light2008 – 2010 1156
Dome Light2000 – 2006 6411
Front Side Marker2000 – 2006, 2008 – 2010 H6W
Front Turn Signal2000 – 2006 H21W
2008 – 2012 PY21W
License Plate2000 – 2006, 2008 – 2012 12844
Parking Light2000 – 2006, 2008 – 2010 H6W
Rear Side Marker2000 – 2006 12961
Rear Turn Signal2000 – 2006 1156
2008 – 2012 921
Tail Light2008 – 2012 1156
2000 – 2006 1157
Courtesy2000 – 2006, 2008 – 2012 6418
Glove Box2000 – 2006 12256
2008 – 2012 12961
Map Light2008 – 2012 12961
Trunk2000 – 2006 12961
2008 – 2012 194
High Beam and Low Beam Headlight2013 – 2015 D1S
Front Fog Light2013 – 2015 H8/H11/H16
Back Up Light2013 – 2015 921
Brake2013 – 2015 1156
Front Turn Signal2013 – 2015 PY21W
Rear Turn Signal2013 – 2015 921
Tail Light2013 – 2015 1156
Glove Box2016 – 2018 12961
2013 – 2015 194
Interior Door2013 – 2018 194
Map Light2013 – 2015 12961
Trunk2013 – 2018 194