Lead Core Line Depth Calculator

Lead Core Line Depth Calculator

Estimate your lure depth based on trolling speed and lead core colors.

(1 color = 10 yards / 30 feet)

Standard range: 1.5 – 3.0 MPH

12 lb 18 lb (Standard) 27 lb 36 lb

Surface / Floating Lure Shallow Diver (+2 ft) Deep Diver (+5 ft)

Estimated Depth: 0 Feet

function calculateLeadCoreDepth() { var colors = parseFloat(document.getElementById('colorsOut').value); var speed = parseFloat(document.getElementById('boatSpeed').value); var weight = parseFloat(document.getElementById('lineWeight').value); var lureExtra = parseFloat(document.getElementById('lureType').value); if (isNaN(colors) || isNaN(speed) || colors <= 0 || speed <= 0) { alert("Please enter valid numbers for colors and speed."); return; } // Industry standard: 5 feet of depth per color at 2.0 mph for 18lb lead core. // Depth is inversely proportional to speed. // Weight adjustment: Heavier lines have more lead but more drag. // 18lb and 27lb perform very similarly in depth due to diameter-to-weight ratios. var baseDepthPerColor = 5; // Adjust base depth based on weight (marginal differences) if (weight 27) baseDepthPerColor = 5.5; // Speed formula: (Colors * Base) * (StandardSpeed / CurrentSpeed) var calculatedDepth = (colors * baseDepthPerColor) * (2.0 / speed); // Add lure contribution var totalDepth = calculatedDepth + lureExtra; document.getElementById('depthOutput').innerText = totalDepth.toFixed(1); var warningText = "At " + speed + " MPH, your " + colors + " colors of " + weight + "lb lead core will reach approximately " + totalDepth.toFixed(1) + " feet deep. "; if (speed > 3.0) { warningText += "Note: High speeds cause lead core to 'lift' significantly due to water resistance."; } else if (speed < 1.5) { warningText += "Note: At low speeds, your lure may sink deeper than estimated as the weight of the lead takes over."; } document.getElementById('resultArea').style.display = 'block'; document.getElementById('depthWarning').innerHTML = warningText; }

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How to Use the Lead Core Depth Calculator

Lead core line is a staple for freshwater trollers targeting Walleye, Trout, and Salmon. Because the line itself is weighted with a lead inner strand, it allows you to get lures down to specific depths without the need for downriggers or heavy snap weights. However, the depth achieved is highly dependent on your boat speed and the amount of line let out.

The Rule of Five

The standard "Rule of Thumb" for lead core (specifically 18lb test) is that you achieve 5 feet of depth for every color (30 feet) of line deployed, assuming a trolling speed of 2.0 MPH. Our calculator uses this physics-based baseline to adjust for faster or slower trolling speeds.

Factors Affecting Lead Core Depth

• Boat Speed: Speed is the most critical variable. As you speed up, water resistance (drag) pushes the line upward. As you slow down, gravity pulls the lead core deeper.
• Line Weight: While 27lb lead core is heavier than 18lb, it is also thicker. The extra thickness creates more drag, which often cancels out the extra weight. This is why 18lb and 27lb often run at similar depths.
• Number of Colors: Lead core is metered every 10 yards (30 feet) with a new color. Counting these colors is the easiest way to track how much line you have deployed.
• Lure Choice: A deep-diving crankbait will pull the lead core deeper than a shallow-running spoon. Our calculator allows you to factor in the lure's native diving ability.

Practical Examples

Colors Out	Speed (MPH)	Estimated Depth
3 Colors	2.0 MPH	15 Feet
5 Colors	2.5 MPH	20 Feet
10 Colors	1.5 MPH	66 Feet

Trolling Tips for Lead Core

To get the most accuracy out of your lead core setup, always use a GPS-based speed over ground (SOG). Small changes in speed (even 0.2 MPH) can move your lure vertically by several feet, potentially taking it out of the strike zone or causing you to snag the bottom. Additionally, remember to use a fluorocarbon leader of 10-20 feet behind the lead core to provide a stealthy presentation to the fish.