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 Headlight 2000 – 2006 H1
2008 – 2009 H7
High Beam Headlight 2000 – 2006, 2008 – 2009 H7
Front Fog Light 2000 – 2006 H3-55W
2008 – 2009 H8/H11/H16
Back Up Light 2000 – 2006 1156
2008 – 2009 921
Brake 2008 – 2009 1156
2000 – 2006 1157
Dome Light 2000 – 2006 578
Front Side Marker 2008 – 2009 12396NA
2000 – 2006 H6W
Front Turn Signal 2000 – 2006, 2008 – 2009 H21W
License Plate 2000 – 2006, 2008 – 2009 12844
Parking Light 2008 – 2009 12396NA
2000 – 2006 H6W
Rear Side Marker 2000 – 2006 12961
Rear Turn Signal 2000 – 2006 1156
2008 – 2009 921
Tail Light 2008 – 2009 1156
2000 – 2006 1157
Courtesy 2000 – 2006, 2008 – 2009 6418
Glove Box 2000 – 2006 12256
2008 – 2009 12961
Map Light 2008 – 2009 12961
Trunk 2000 – 2006 12961
2008 – 2009 194
Low Beam Headlight 2000 – 2006 D2S
High Beam Headlight 2000 – 2006 H7
High Beam and Low Beam Headlight 2008 – 2009 D1S
Front Fog Light 2000 – 2006 H3-55W
2008 – 2009 H8/H11/H16
Back Up Light 2000 – 2006 1156
2008 – 2009 921
Brake 2008 – 2009 1156
2000 – 2006 1157
Daytime Running Light 2008 – 2009 1156
Dome Light 2000 – 2006 6411
Front Side Marker 2000 – 2006, 2008 – 2009 H6W
Front Turn Signal 2000 – 2006 H21W
2008 – 2009 PY21W
License Plate 2000 – 2006, 2008 – 2009 12844
Parking Light 2000 – 2006, 2008 – 2009 H6W
Rear Side Marker 2000 – 2006 12961
Rear Turn Signal 2000 – 2006 1156
2008 – 2009 921
Tail Light 2008 – 2009 1156
2000 – 2006 1157
Courtesy 2000 – 2006, 2008 – 2009 6418
Glove Box 2000 – 2006 12256
2008 – 2009 12961
Map Light 2008 – 2009 12961
Trunk 2000 – 2006 12961
2008 – 2009 194
Low Beam Headlight 2000 – 2006 H1
2008 – 2012 H7
High Beam Headlight 2000 – 2006, 2008 – 2012 H7
Front Fog Light 2000 – 2006 H3-55W
2008 – 2012 H8/H11/H16
Back Up Light 2000 – 2006 1156
2008 – 2012 921
Brake 2008 – 2012 1156
2000 – 2006 1157
Dome Light 2000 – 2006 578
Front Side Marker 2008 – 2012 12396NA
2000 – 2006 H6W
Front Turn Signal 2000 – 2006, 2008 – 2012 H21W
License Plate 2000 – 2006, 2008 – 2012 12844
Parking Light 2008 – 2012 12396NA
2000 – 2006 H6W
Rear Side Marker 2000 – 2006 12961
Rear Turn Signal 2000 – 2006 1156
2008 – 2012 921
Tail Light 2008 – 2012 1156
2000 – 2006 1157
Courtesy 2000 – 2006, 2008 – 2012 6418
Glove Box 2000 – 2006 12256
2008 – 2012 12961
Map Light 2008 – 2012 12961
Trunk 2000 – 2006 12961
2008 – 2012 194
Low Beam Headlight 2000 – 2006 D2S
High Beam Headlight 2000 – 2006 H7
High Beam and Low Beam Headlight 2008 – 2012 D1S
Front Fog Light 2000 – 2006 H3-55W
2008 – 2012 H8/H11/H16
Back Up Light 2000 – 2006 1156
2008 – 2012 921
Brake 2008 – 2012 1156
2000 – 2006 1157
Daytime Running Light 2008 – 2010 1156
Dome Light 2000 – 2006 6411
Front Side Marker 2000 – 2006, 2008 – 2010 H6W
Front Turn Signal 2000 – 2006 H21W
2008 – 2012 PY21W
License Plate 2000 – 2006, 2008 – 2012 12844
Parking Light 2000 – 2006, 2008 – 2010 H6W
Rear Side Marker 2000 – 2006 12961
Rear Turn Signal 2000 – 2006 1156
2008 – 2012 921
Tail Light 2008 – 2012 1156
2000 – 2006 1157
Courtesy 2000 – 2006, 2008 – 2012 6418
Glove Box 2000 – 2006 12256
2008 – 2012 12961
Map Light 2008 – 2012 12961
Trunk 2000 – 2006 12961
2008 – 2012 194
High Beam and Low Beam Headlight 2013 – 2015 D1S
Front Fog Light 2013 – 2015 H8/H11/H16
Back Up Light 2013 – 2015 921
Brake 2013 – 2015 1156
Front Turn Signal 2013 – 2015 PY21W
Rear Turn Signal 2013 – 2015 921
Tail Light 2013 – 2015 1156
Glove Box 2016 – 2018 12961
2013 – 2015 194
Interior Door 2013 – 2018 194
Map Light 2013 – 2015 12961
Trunk 2013 – 2018 194