How long was Hitler a dictator?

Hitler officially came to power on January 30, 1933; however, he still had to deal with other politicians, so he wasn't fully dictator yet. It took over a year to complete the transition, which ended on August 2, 1934 when President Hindenburg died. He remained absolute dictator for the rest of his life, which ended when he committed suicide on April 30, 1945.

So, the time from August 2, 1934 to April 30, 1945 is roughly 11 years, 8 months and 28 days, without factoring in oddball stuff like leap years.