Fish Length Measurements

The following six metrics are the most commonly used for measuring the length of tunas, billfish, other bony fish, sharks, rays, and turtles. Ideally, the observer has a set of calipers and a slate, waterproof paper, or other writing options for wet work.

Fork Length ("FL")

• Measurement: The length from the snout to the fork in the tail.
• Uses: For all tunas and other fish with a fork in the tail (including sharks).

Lower Jaw to Fork ("LF")

• Measurement: The length from the lower jaw to the fork in the tail.
• Uses: For billfish.

Total Length ("TL")

• Measurement: The total length of the fish.
• Uses: For all species with no fork in the tail.

Total Width ("TW")

• Measurement: Total width of fish.
• Uses: For rays.

Carapace Length ("CL")

• Measurement: Length of animal's carapace.
• Uses: For turtles.