Well, I would say before it was a bit more than 1/2 inch, and now, with a gradual change over a period of about 2 months, it is a bit more than 1/4 inch. This is my estimation, (I didn't actually get out a ruler and measure). I have been playing Trumpet for almost 2 years now, and before that I played Saxophone for a year and 1/2, then I played Trombone and Tuba for a good 6 or 7 months, then I started on Trumpet and I haven't looked back since.
I am in the Wind Ensemble at my High School and my range is high B. My range used to be comfortably to a high C, but that was before my embouchure change. About 2 months ago, with the help of my teacher, I began to correct my roll-in embouchure. My top lip rolled in excessively and I was also using to much pressure to compensate for this. Then I started free-buzzing and I simply applied that embouchure to my playing. My tone and consistancy have improved.My range, while my overall tone is better, is not quite what it was, but that is a temporary sacrifice I am willing to accept for the purpose of good tone.