The generally accepted value of an airline frequent flyer mile is 2 cents!
To look at that from a practical point of view - if it takes 25,000 frequent flyer miles to get a round trip ticket, you're paying about $500 for that ticket. Here's where you need to be smart and make a good decision - for example, with a 21-day advance purchase you can buy a ticket to fly round-trip between Newark and and Ft. Lauderdale for about $170. I absolutely wouldn't use my miles for those flights. However - if you haven't planned for that trip and must purchase your ticket at the last minute, those same flights could cost well over $600. That's where you get good value from your miles -paying the equivalent of $500 for a $600+ ticket.
Let me give you a another example: my wife and I are going on a cruise in South America next year. We used 180,000 miles each for a 1st Class round-trip ticket. That's the equivalent of $3600. However, the actual cost of a round-trip ticket in 1st class is over $8300! We got the equivalent of 4.15 cents per mile! That over double the accepted value.
I hope this information was helpful
I am a Certified Travel Consultant Specialist and very frequent flyer.