Below is a list of light bulb types used in 2018- AUDI Q3 lighting system, covering SUV and SUV vehicles.
Rear indicator/turn signal bulb: PY21W
Tail light bulb: W5W
Brake light bulb: P21W
Back-up light bulb: W16W
Rear fog light bulb: H21W
Light bulb sizes for other AUDI Q3 generations: Q3 (8U)