A hobby metal detector depth guide.

The ultimate question always asked by those new to the hobby is always – “How deep can a metal detector detect?”

So how deep can they detect? and what factors affect this? It can be a complex answer.

Two Categories affecting metal detector depth:

External Factors (Not related to the detector itself)

• Depth of the metal object.
• Soil type.  How aerated or compacted is the soil and how much mineralisation is present in the soil.
• Slope of the ground. Ground angle can affect depth as object may get buried deeper and angle of detection may create more ground between the coil and metal target.
• Size of metal object. Larger objects can be detected deeper.
• Type of metal. Some metals are more conductive and can be picked up deeper.
• Rainfall. Wet ground is more difficult to detect deeper and frequently wet ground allows objects to sink deeper quicker over time.

Internal Factors (the metal detector itself).

• Coil size. Generally for the beat frequency detectors like the Ace, depth of detection is close to or just over the width of the coil. A larger coil will give greater depth but sensitivity and accuracy may be lost the larger you go.
• Type of technology. Pulse induction detects deeper than Beat frequency and is less effected by ground minerals. Learn more about pulse induction v.s. Beat frequency here.
• Frequency. All detectors operate at different frequencies. Low = greater depth but less sensitivity. High = great sensitivity but less depth. Some detectors have a combination getting the best of both. Learn more on frequency here.

Important considerations:

• Lost coins and battlefield relics are often much shallower than people first think.
• Generally speaking a ring or coin lost on the surface around 100 – 200 years ago will only sink to around 3 – 20 cm over time.
• This is why hobby detectors are specially designed to be more accurate at this depth range!!! 
• Some relics are often found on the surface after over 100 years under the sun. soil, rainfall etc all determine the depth the item will sink.
• Going deeper than around 30 cm means you will have less and less luck as it is highly unlikely that objects of interest sank deeper unless deliberately buried.

Better accuracy at this depth range is a more important consideration than depth when hobby detecting.  

Special note on beach detecting and depth:

• A detector will always get greater depth at the beach due to aeration of the sea sand.
• However items can get buried much deeper due to wave action and storms. Thus you may want a machine that can go deeper at the beach but there will still be plenty near the surface. You can also wait for storms to uncover deeper items. A beach with rough waves and steep incline will bury items deep quickly. Seek out flat protected beaches.  More on beach detecting.

A rough depth guide:

No manufacturer can guarantee a depth however due to the factors above but this may be used as a rough guide – Please bear this in mind to avoid disappointment.

• Small jewelry (e.g., necklaces and thin gold rings) at 7 – 15 cm
• Big jewelry (e.g., class ring) at 15 to 30 cm
• Small coins (e.g., Ticky, 1 cent) at 10 to 15 cm 
• Large coins: (e.g., Kruger pond, 5 shilling) at 15 to 30 cm
• Jam jar lid,  bicycle licence disc at 22 to 40 cm
• Coffee can size at 30 to 60 cm
• Cannon shell, etc. at 60 to 90 cm

Gold Prospecting is different. – Learn about gold prospecting and depth here.

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