Lure Trolling Depth Calculator
Estimate how deep a lure runs when trolling based on line diameter, trolling speed, and amount of line out.
Plan your trolling presentation.
When trolling, the depth a lure runs depends on the line diameter (which creates water resistance and drag), the amount of line out, and the trolling speed. Faster speeds push lures shallower; thinner line allows them to run deeper.
Simplified depth formula: Depth ≈ (Line out in feet ÷ 10) × line factor ÷ speed factor
The line factor is 1.0 for thin mono or braid, 0.85 for standard mono and 0.70 for heavy mono, because a fatter line drags more water and holds the lure up. The speed factor is 1 + 0.15 × (mph − 2), so it is exactly 1.0 at 2 mph and grows from there.
This is an approximation. Actual depth varies significantly by lure type, weight, and lip angle. Manufacturers publish depth charts for specific lures (e.g., Rapala, Bomber), and those beat any general formula. Divers and weight systems (snap weights, downriggers) reliably control depth.
General rule of thumb for crankbaits:
- Every 10 ft of monofilament out: dives ~1 ft (slow, thin line)
- With 0.008" diameter mono at 2 mph: roughly 1 ft per 10 ft of line
- With 0.011" mono: roughly 1 ft per 12 ft of line
- Each extra mph above 2 mph costs about 13% of the depth in this model
That last one surprises people. Speed changes depth far less than line diameter does, at least for a diving crankbait pulling against its own lip. Going from 2 to 3 mph takes roughly an eighth off the depth, not a third. Lead-core and snap-weight rigs behave the other way around: they have no lip to bite with, so speed lifts them much harder, and this calculator does not model them at all.
Depth control options:
- Lead core line: color-coded, each color is 10 yards, dives about 5 ft per color
- Snap weights (in-line weights): add 1–3 oz to run 5–15 ft deeper
- Downriggers: precise depth control, lure releases at strike
- Diving planes (Dipsy Divers): run 30–60 ft deep
The best approach: use a depth finder to confirm fish location, then adjust presentation until you match that depth.
How we build and check this calculator
This calculator runs entirely in your browser, so the numbers you enter stay on your device. The math behind it is written by hand and tested against worked examples and standard references before the page goes live.
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