How deep does a metal detector actually detect?

Technique & settings · Published Nov 2, 2026

The common mistake is believing there is one depth number for a metal detector, and then shopping for the machine with the biggest one. Start with the disagreement instead. Garrett, a manufacturer, says detectors are typically capable of uncovering objects buried between 10 and 16 inches deep. Minelab, another manufacturer, says that for coin sized targets most high performance detectors locate objects between 6 and 12 inches deep in optimal conditions. Serious Detecting, an independent retailer guide, says most modern hobby detectors with the stock coil find coin sized targets at about 6 to 10 inches in average soil. Three honest sources, three ranges, and none of them is lying. They are measuring different things.

What the published ranges actually measure

Garrett's range is a capability statement across target sizes: the same page notes that very large coils or two-box detectors can detect targets several feet down, which is true of cache sized metal and irrelevant to a dime. Minelab's range is narrower because it names its target, a coin, and its condition, optimal ground. Serious Detecting's range is the field number: a stock coil of about 9 to 11 inches, moderate ground, a coin lying flat. Put the three side by side by target and the conflict mostly dissolves:

One more number inflates expectations before any of these apply: the air test. Serious Detecting states plainly that air tests overstate depth, often by a few inches or more, because air offers no mineralization to fight. A detector that beeps on a coin at 14 inches on a workbench has promised nothing about your park.

The five things that move the number

Target size and shape. Bigger targets return more signal and read deeper, on every source. Orientation matters too: a coin lying flat reads deeper than the same coin standing on edge.

Target metal. Minelab notes that highly conductive metals such as silver and copper produce stronger signals and better depth, while lower conductivity metals such as gold are harder to detect at depth.

The ground. Highly mineralized soil weakens signals; Serious Detecting puts the cost at a third or more of typical depth. Moist soil often improves conductivity and helps depth, per Minelab, which is one reason the same field hunts deeper after rain than in a dry spell.

Coil size. Garrett's rule of thumb ties depth to coil diameter: a 4 inch coil might find a standard coin at about 4 inches, a 12 inch coil the same coin at about 12 inches, with no further gain for that coin beyond that point. The trade runs both ways. Minelab notes larger coils suit open areas and depth, while smaller coils give better sensitivity to small, shallow targets in trashy or confined areas and suffer less electromagnetic interference.

Settings and frequency. Sensitivity helps until it hurts: Serious Detecting advises running it as high as the detector stays quiet and stable, because maximum sensitivity in noisy ground often finds less. Garrett adds that too much sensitivity produces false signals in mineralized soil. On frequency, both manufacturers agree on the direction: lower frequencies suit larger, deeper, high conductivity targets, and higher frequencies are more sensitive to small, shallow, low conductivity items such as fine gold.

Measure your own machine: a buried coin depth check

The published ranges describe other people's ground. This check takes an hour in a yard or any ground you have permission to dig, and replaces all three ranges with your number.

1. Pick clean ground. Sweep the patch first and choose a spot with no signals, so every beep during the check is a coin you placed.
2. Bury four coins flat. Use the same coin type for all four, laid flat at measured depths of 4, 6, 8, and 10 inches, spaced far enough apart that the coil sees one at a time. Measure from the surface to the coin, not to the top of the hole.
3. Replace and pack the soil. Fill each hole and firm the soil back down. Loose, freshly turned soil reads differently from settled ground, and packing narrows the gap.
4. Set the machine up properly. Ground balance on that soil first, then set sensitivity as high as the detector stays quiet and stable over the clean patch.
5. Sweep each coin at hunting speed. Note the deepest coin that gives a repeatable signal from two directions, and the deepest that gives a signal you would actually stop and dig. Record both numbers; they are rarely the same.
6. Turn one coin on edge and repeat. The edge reading shows, on your own machine, how much of the published depth depends on a coin lying flat.

What success looks like: a written pair of numbers, repeatable depth and diggable depth, for your detector, your coil, and your soil. If the diggable number sits far below the repeatable one, the limit is signal quality, not reach, and settings work will pay better than a bigger coil.

When depth is the wrong thing to chase

Most lost coins and jewellery were dropped, not buried by a glacier, and they sit in the top few inches for years before soil movement takes them down. A trashy park rewards separation and a small coil more than raw depth, and mineralized ground taxes depth no matter the machine. Buy and set up for the ground you actually hunt. The honest depth figure is the one from the buried coin check, and for most Canadian parks it will land inside the 6 to 10 inch field range, which is exactly deep enough for the targets that are actually there.

, Tom Reilly, Home & DIY Writer