How can I get the number of frames per second from a gif file?

A GIF file doesn't contain an FPS value, rather each frame contains a duration.

Each frame contains a header.

Hex Byte Number 324 contains the frame duration in 100ths of a second, for example 09 00 would be 0.09 seconds.

EDIT: reference http://en.wikipedia.org/wiki/Graphics_Interchange_Format#Animated_GIF