This is a bio of the FAA requirements for obtaining each license. From a new Pilot flying for fun on vacation to the Profressional Pilot flying for a living!!
Private Pilot: Minimum's
 Total Flight Time
Total Flight Time 40 hours
40 hours
Which includes the below times:
 Dual FlightTime
Dual FlightTime 20 hours
 20 hours
 Solo Flight Time
Solo Flight Time 10-15 hours
10-15 hours
 Ground Instruction     15 hours (as required)
Ground Instruction     15 hours (as required)
Instrument Pilot: Minimum's
 Total Flight Time
Total Flight Time 40 hours (actual or simulated instrument conditions)
40 hours (actual or simulated instrument conditions)
Which includes the below times:
 Dual Instruction
Dual Instruction 20-30 hours
  20-30 hours
 Simulator
Simulator
 20 hours (Maximum)
    20 hours (Maximum)
 Ground Instruction     15-20 hours (as required)
Ground Instruction     15-20 hours (as required)
 Dual XC Time**
Dual XC Time** 5 hours
    5 hours
**Must have a Private Pilot and have completed 50 hours of Cross Country Pilot in Command time at Completion of Instrument Rating.  
Commercial Pilot: Minimum's
 Total Flight Time
Total Flight Time 20 hours (Complex Aircraft)
20 hours (Complex Aircraft)
 Dual Flight Time
Dual Flight Time 10 hours (Complex Aircraft)
 10 hours (Complex Aircraft)
 Dual XC Time
Dual XC Time 9 hours
       9 hours
**Must have a Private Pilot and have completed 250 hours Total Time, 100 hours of Pilot in Command time and 50 Cross Country time at Completion of Commercial Rating.
Certifited Flight Instructor  Minimum's
 Dual Instruction
Dual Instruction 10-20 hours (Average)
10-20 hours (Average)
 Ground Lessons
Ground Lessons 20 hours
20 hours
**Must have a Commercial Pilot  and Instrument Pilot Completed
Certified Flight Instructor Instrument Minimum's
 Dual Instruction
Dual Instruction 10-20 hours (Average)
10-20 hours (Average)
 Ground Lessons
Ground Lessons 20 hours
20 hours
**Must have a Commercial Pilot and Instrument Pilot Completed