Airplane sizes

[Klonas]

Could someone explain me the airplane and motor sizes?
I often see something like this:
Recommended 60 size motor
.60 Glow
120 size Extra 300 (plane)
I don't really understand what those sizes are and mean...

 

[pgerts]

There has been some practical sizes based on the size, weight and use of the model.
.15 - normally small planes and combat less than 1 m span - sport up to 1,3 m span.
.25 - next size bigger combat and trainers up to 1,5 meter span
.40 - "normal" trainer up to 1,8 meter span.
.60 - F3A pattern planes from 70´s and 80´s
Old scale sport planes are normally larger
Fighter normally smaller
Electric can be compared to old - example 25e size, but today most planes are recommended in electric watt.