Ah, itty bitty reels.
Rough guide for 35mm
Reel Diameter Footage Length Running Time
4 in 100 ft 1 min
6.5 in 400 ft 4 min
10.5 in 1000 ft 11 min
11.5 in 1200 ft 13 min
13 in 1600 ft 17 min
14.5 in 2000 ft 22 min
16 in 3000 ft 33 min