It's a handy one because in addition to AWG size, diameter, Ohms, and Amperes, it also has frequency limits for 100% skin depth on solid conductors.
You might want to read through this page: http://www.dos4ever.com/flyback/flyback.html
It's for low-current high-voltage flyback converters, but there's some good info on using ferrites in winding transformers/inductors for power supplies, and testing them.