Film is charged by the foot.  Small reels that fit into the palm of your hand are 50 foot reels.  The larger reels sometimes have the footage marked on the reel.
 
8mm, Super 8mm, & 16mm Film Conversion 
(Minimum charge of $25.00 for 50 foot roll) 
< 1000 feet                                $0.65/foot 
1001-2000 feet                         $0.62/foot
2001-5000 feet                         $0.59/foot