When doing replacement or upgrading on 2013 – 2018 Cadillac ATS with capsule halogen headlamps HID, the bulb size guide is necessary for you to take the reference.
Jump to corresponding car model with the catalog bellow.

High Beam and Low Beam Headlight2013 – 2018 9012
Back Up Light2013 – 2018 921
Front Side Marker2013 – 2018 194
Front Turn Signal2013 – 2018 7444NA
License Plate2013 – 2018 194
Parking Light2013 – 2018 7443NA
High Beam and Low Beam Headlight2013 – 2018 D3S
Back Up Light2013 – 2018 921
Front Side Marker2013 – 2018 194
Front Turn Signal2013 – 2018 7444NA
License Plate2013 – 2018 194
Parking Light2013 – 2018 7443NA