I would put him at around the 5'7" mark (1.70m). I am basing this on the photo of him below standing on the far right next to Ben McKenzie who is 5'8" (1.73m).
Robin Lord Taylor looks to be about an inch shorter than him. The other person in the photo is Donal Logue who is 5'11" (1.8m)
All three actors appear in the American crime drama series 'Gotham' which is based on the 'Batman' story created by DC comics which began in 1940. It is quite an accomplishment for an idea that started out that long ago to still be very popular today.The series tells the story of not only the character of Batman, but also many of the villains including Catwoman, Joker, Riddler and of course Penguin played by Robin Lord Taylor.
It's one of the best shows on TV at the moment, and I recently read that Netflix had purchased the rights to stream it too!