In search of wisdom: Choosing the best headlight bulb size

Hello, forum friends! I recently bought a used car, and it seems that the previous owner installed aftermarket headlights with a different bulb size. How can I determine the original headlight bulb size recommended by the car manufacturer for optimal performance and compatibility?

Your advice is an absolute treasure that I hold in high regard! The immense sense of relief and gratitude I'm currently experiencing is beyond measure. Your guidance has been an incredible blessing, as it not only saved me precious time but also steered me clear of impulsive purchases that often bring about regret. Thank you sincerely!