When doing replacement or upgrading on 2017 – 2018 Hyundai Ioniq 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.

Low Beam Headlight 2017 – 2018 H7
High Beam Headlight 2017 – 2018 9005
Back Up Light 2017 – 2018 921
Brake 2017 – 2018 1157
Dome Light 2017 – 2018 DE3175
Front Side Marker 2017 – 2018 168
Front Turn Signal 2017 – 2018 2357NA
License Plate 2017 – 2018 168
Parking Light 2017 – 2018 168
Rear Side Marker 2017 – 2018 168
Rear Turn Signal 2017 – 2018 1156
Tail Light 2017 – 2018 1157
Trunk 2017 – 2018 DE3423
High Beam and Low Beam Headlight 2017 – 2018 D3S
Back Up Light 2017 – 2018 921
Dome Light 2017 – 2018 DE3175
Front Side Marker 2017 – 2018 194
Front Turn Signal 2017 – 2018 2357NA
License Plate 2017 – 2018 168
Trunk 2017 – 2018 12844