How much time served on an 11 year prison sentence?

In the UK, normally the sentence actually served is two thirds, but this is dependent on parole or judge's instructions. Probably around 7 - 8 years with good behavior.

In the US some states award time for good behavior, some states have minimum sentencing laws. The typical US criminal sentence will have two time periods, the minimum and the maximum. The minimum will be anywhere from more than a year to 40 or more years. The maximum will be anywhere from more than a year to life. The only sentence in the US that is not issued without a minimum is "Life without the possibility of parole."

In a state that follows minimum sentence laws, if the minimum sentence is 11 years, the offender will serve 11 years.