Leticia says on 1/Feb/12
In the season 8 episode "Hooping Cranes," when Niles, Frasier, and Martin enter the apartment after Niles makes that half-court shot at the Seahawks game, Frasier says, "Now entering the apartment, a 5'9" psychiatrist from Seattle, Niles Crane!" And in the season 1 episode "You Can't Tell a Crook by His Cover," Niles says that Daphne is 5'9" and 3 quarters.

Jessie says on 31/Dec/10
when him and Jane are barefoot in 'The Ski Lodge' he IS taller- about half and inch- which I think makes him an even 5-10 if not 5'10 1/2. otherwise she would look much taller than him in heels if he was only 5'9.