What do fly line sink types mean?

Sink types describe how fast a line drops in inches per second. Type 2 sinks about 2 IPS, Type 3 about 3 IPS, and so on up to Type 7 at roughly 7 to 8 IPS. Higher numbers reach deeper water faster, which matters for streamers and stillwater fishing.

How is sink depth calculated?

Depth before retrieving is simply sink rate times countdown time: a 4 IPS line sinking for 20 seconds reaches about 80 inches, or roughly 6.7 feet. The tool then subtracts a lift factor based on your retrieve speed, because stripping line pulls the fly upward.

Why does retrieve speed reduce depth?

A sinking line keeps falling only while it sits still. Once you strip, the fly planes upward, so a fast retrieve fishes shallower than the static countdown depth. The faster you strip, the more lift, which is why a slow, deep crawl reaches the bottom and a quick retrieve stays high.

What is the countdown method?

You cast, then count seconds before starting your retrieve, letting the line sink a predictable amount each second. By increasing the count until you find fish, you can repeat the exact depth that produced a strike. This calculator turns your count into a depth estimate.

Does line density and current change the depth?

Yes. These figures assume still water and a fully sunk line. Current, a floating leader, and a buoyant fly all reduce real depth, while a heavy weighted fly increases it. Use the estimate as a starting point and adjust your countdown based on what you feel and catch.

Fly Line Trolling Depth Calculator

Knowing how deep your fly is running is the key to streamer and stillwater success. This calculator turns a sinking line’s inches-per-second (IPS) rate and your countdown time into a depth estimate, then adjusts for how fast you retrieve.

How it works

Static sink depth grows linearly with the countdown, and the retrieve lifts the fly:

staticDepth (ft) = (IPS × countdownSeconds) / 12
liftFactor       = retrieveSpeed scaled 0 (dead-drift) … ~0.5 (fast strip)
fishingDepth     = staticDepth × (1 − liftFactor)

Sink types map to IPS roughly as: Type 2 ≈ 2, Type 3 ≈ 3, Type 4 ≈ 4, Type 5 ≈ 5, Type 6 ≈ 6, Type 7 ≈ 7.5. The longer you count down, the deeper the line; the harder you strip, the more the fly planes back toward the surface.

Example and tips

A Type 4 line (4 IPS) counted down 30 seconds reaches 4 × 30 / 12 = 10 feet static. With a moderate retrieve (lift factor ≈ 0.25) it fishes around 7.5 feet. Use the countdown method to bracket depth: add five seconds to your count until you find fish, then repeat that exact count. Remember these numbers assume still water — current and a buoyant fly will keep you shallower than the estimate.