The length of the fallopian tube is:
Important Facts about Fallopian Tube:
Length = 4 inches or 10-12 cm.
Parts are :

Interstitium (Intramural): 1.8 cm long and 1 mm diameter (narrowest partQ). It has no longitudinal muscles, only circular muscles are present.Q
Isthmus: 3.5 cm long and 2 mm in diameter.Q (Second narrowest partQ).
Ampulla: widestQ and longest partQ 6-7.5 cm and fertilization occurs hereQ
Fimbria/infundibulumQ

Histologically:

Fallopian tubes have unique type of cells called as Peg cellsQ whose function is not known.Q
8 - 10 cm
10 - 12 cm
15 - 18 cm
18 - 20 cm