Metal Detector Coil Sizes Explained: Small vs Large Coils 

Most metal detectors come supplied with a general-purpose search coil designed to work well across a wide range of conditions.

But that doesn't necessarily mean the standard coil is the best option for every site.

Move onto a field littered with iron and a smaller coil can completely change what you're able to hear. Walk onto acres of relatively clean pasture and a larger coil can help you cover more ground while potentially improving your chances of detecting deeper targets.

So what actually changes when you fit a different-sized coil?

And does fitting the biggest coil available automatically mean you'll find deeper targets?

Not quite.

Understanding the advantages and compromises of different coil sizes can help you choose the right setup for the ground you're detecting, rather than simply assuming bigger is always better.

What Does the Search Coil Actually Do?

The search coil is the part of your detector that interacts with the ground.

It contains windings used to transmit an electromagnetic field and receive the response produced when that field interacts with a metallic target.

Your detector processes that response and turns it into the audio, Target ID and other information you see or hear.

Changing the coil therefore changes more than simply the physical footprint at the bottom of your detector.

Coil size and shape can influence:

• Detection depth
• Ground coverage
• Target separation
• Sensitivity to smaller targets
• Performance in difficult ground
• Manoeuvrability
• Weight and balance

If you're using a Minelab detector and aren't sure which accessory coils are compatible with your machine, we've also put together a full Minelab Coil Compatibility Guide.

Small, Medium or Large – What Counts as Each?

There isn't an official industry-wide definition of a small, medium or large metal detector coil.

However, for the type of detectors commonly used for UK coin and artefact hunting, a rough guide would be:

Coil size	Typical use
Small – around 5–8 inches	Iron, rubbish, woodland and tight spaces
Medium – around 9–11 inches	General-purpose detecting
Large – around 12–15+ inches	Open ground, greater coverage and deeper targets

Elliptical coils may have two measurements instead of one, such as 8 x 5.5 inches or 15 x 12 inches.

Modern detectors often have accessory coils covering most of this range.

For example, the Minelab MANTICORE platform includes the compact M8 8 x 5.5-inch coil, the M9 9-inch, standard M11 11-inch, and larger M15 15 x 12-inch coil.

Nokta takes a similar approach with the LEGEND 2, with several coil sizes available to suit different types of detecting.

That range exists for a reason.

No single coil is best everywhere.

Small Metal Detector Coils

A small coil can look like a downgrade when you're used to swinging an 11-inch coil.

In the right conditions, though, it can be exactly the opposite.

Better Target Separation

One of the biggest advantages of a smaller coil is its ability to investigate ground containing several targets close together.

Imagine a small silver coin sitting just a few centimetres away from an iron nail.

With a larger coil, both objects may fall within the detector's active search area at the same time. The strong response from the iron can interfere with the detector's ability to recognise the desirable target sitting alongside it.

This is commonly known as target masking.

A smaller coil examines a smaller area of ground at any one moment, which can make it easier to isolate the non-ferrous target from nearby iron.

This can be particularly useful around:

• Old habitation sites
• Gateways
• Field entrances
• Demolished buildings
• Medieval settlement areas
• Old footpaths
• Areas containing large quantities of iron

It's also one reason changing to a smaller coil can sometimes produce more finds from an area you thought had already been thoroughly searched.

The target wasn't necessarily too deep.

It may simply have been difficult for the detector to separate from everything surrounding it.

Closely spaced targets can also cause Target IDs to become less stable or misleading. If you're unsure what the numbers on your detector are actually telling you, take a look at our Metal Detector Target IDs Explained guide.

Small Coils and Tiny Targets

Smaller coils can also perform extremely well on small targets.

That can include small hammered coins, tiny fragments of non-ferrous metal and other weak targets that might otherwise be difficult to isolate.

This doesn't mean a small coil is automatically more sensitive to every tiny object than every larger coil. Detector design, operating frequency, settings, ground conditions and the coil itself all play a part.

The important point is that a small coil often allows the detectorist to work more precisely.

On a busy site, being able to isolate a tiny target can be more valuable than having maximum outright depth.

Easier Around Stubble and Obstacles

There's also a much simpler advantage.

A small coil physically fits into places that a big one doesn't.

Thick stubble, woodland, roots, bushes, deep furrows and uneven ground can make controlling a large coil frustrating.

A small elliptical coil can often be worked between those obstacles while remaining much closer to the soil.

And keeping the coil close to the ground matters.

There's very little advantage in having a theoretically deeper coil if you're constantly swinging it several inches above the surface because it keeps catching on vegetation or stubble.

Where We'd Use a Small Coil

A compact coil is particularly worth considering when detecting iron-infested ground, woodland, heavy stubble, old habitation areas, awkward terrain or anywhere containing lots of closely spaced targets.

The Minelab M8, for example, is an 8 x 5.5-inch elliptical DD coil designed for the MANTICORE and is particularly well suited to tight spaces and sites where target separation matters.

Standard or Medium-Sized Coils

There's a reason manufacturers commonly supply something around the 9–11-inch mark as the main coil with a detector.

It's the compromise.

A medium-sized coil usually gives you a good combination of:

• Depth
• Ground coverage
• Target separation
• Manageable weight
• Manoeuvrability

For typical UK detecting across pasture, ploughed fields, stubble and relatively clean farmland, that middle ground can be extremely difficult to beat.

If you're only going to own one coil, the standard coil supplied with a good modern detector is usually the logical place to start.

Learn what it can do first.

You may eventually discover that one particular permission would benefit from something more specialised, but don't feel as though an accessory coil is essential before you've properly learned the standard one.

Large Metal Detector Coils

Then we come to the big ones.

A 13, 14 or 15-inch coil hanging off the end of a detector certainly looks serious.

And large coils have some genuine advantages.

But they also come with compromises.

Do Larger Coils Detect Deeper?

Generally, a larger coil can provide additional depth – particularly on medium and larger targets – but it isn't quite as simple as bigger coil equals deeper finds.

Fitting a 15-inch coil does not suddenly mean every coin becomes detectable several inches deeper.

Real-world detection depth depends on many factors, including:

• Target size
• Target orientation
• Metal composition
• Soil mineralisation
• Ground moisture
• Detector settings
• Electromagnetic interference
• Search mode
• How close you can keep the coil to the ground

We've covered those variables in much more detail in our How Deep Can a Metal Detector Really Detect? guide.

A larger coil is therefore better viewed as something that can improve depth under the right conditions, rather than as a guaranteed depth upgrade.

A large coil also tends to show its advantage more clearly on larger targets than it does on extremely small ones.

Greater Ground Coverage

One of the most useful advantages of a large coil has nothing to do with depth.

It's coverage.

Walk across a huge open field with a small coil and you're examining a relatively narrow strip of ground with every sweep.

Increase the physical dimensions of the coil and you're able to cover a wider area with each pass.

Over several hours, that can make a considerable difference.

This is where something like a 15 x 12-inch coil starts to make sense.

Large, relatively clean areas such as:

• Pasture
• Cultivated fields
• Stubble
• Beaches
• Rally fields

can all suit a larger coil.

If you've got acres of ground to search and relatively little iron or modern rubbish, extra coverage can sometimes be as useful as any potential improvement in depth.

Why Isn't Everyone Using the Biggest Coil Possible?

Because every advantage comes with a compromise.

More Targets Under the Coil

A large coil doesn't only see more potentially interesting targets.

It also sees more unwanted metal.

Take a clean pasture field and this may not be much of an issue.

Move onto an old habitation site full of nails and fragments of iron and things become much more complicated.

A large coil may have several metallic objects underneath it during a single sweep.

That means the detector could be trying to interpret responses from iron, a desirable non-ferrous target and more iron in a very small area.

This is where the precision offered by a smaller coil becomes valuable.

A larger coil may technically be capable of detecting the coin at greater depth under ideal conditions, but that doesn't necessarily help if the target is being masked by nearby iron.

Mineralised Ground

A larger coil also interacts with a greater volume of ground.

Where soil is highly mineralised or otherwise difficult, that additional ground response can sometimes make detector operation less stable.

Modern ground balancing systems are extremely capable, but there are still situations where a smaller coil can simply be easier to control.

If difficult ground forces you to significantly reduce sensitivity to make the detector stable, some of the expected advantage of using a bigger coil may disappear.

Electromagnetic Interference

Electromagnetic interference, usually shortened to EMI, can also affect detector stability.

Possible sources include:

• Overhead power lines
• Underground electrical cables
• Electric fences
• Mobile phone equipment
• Nearby electronic devices
• Other metal detectors

Changing coil size won't magically fix EMI, but different coils can sometimes behave differently in the same environment.

If fitting a larger coil results in a noisier detector and you have to heavily reduce sensitivity to compensate, that needs to be weighed against any potential depth benefit.

Weight and Fatigue

Then there's the part manufacturers can't completely engineer away:

Your arm.

A bigger coil will normally increase overall weight and, more importantly, move additional weight towards the end of the detector shaft.

Even if the difference doesn't feel dramatic when you first pick the machine up, it may feel very different after four or five hours.

Fatigue can affect:

• Sweep speed
• Coil control
• Coil height
• Overlap between swings
• How level the coil remains
• How long you actually want to keep detecting

A technically deeper coil that you're lifting several inches at the end of every swing isn't necessarily going to outperform a smaller coil being kept level and close to the ground.

Comfort is part of performance.

Coil Size and Ground Coverage: Don't Forget Your Sweep

A larger coil won't compensate for poor detecting technique.

Whatever coil you're using, adjoining sweeps should overlap.

If each swing simply touches the edge of the previous one, it's very easy to leave strips of ground insufficiently searched.

Targets don't conveniently sit directly underneath the centre of every sweep either.

Maintaining a slow, controlled swing while overlapping each pass can make a huge difference to how thoroughly you're searching a site.

Sometimes the best way to find more isn't to buy a bigger coil.

It's to slow down with the one you've already got.

What About Round vs Elliptical Coils?

Size isn't the only difference between coils.

Shape matters too.

Two coils can have similar overall surface areas but feel very different in use.

Round Coils

Round coils are extremely common and work particularly well as general-purpose search coils.

They're simple to control and give consistent coverage when detecting open ground.

Elliptical Coils

An elliptical coil can be particularly useful where manoeuvrability matters.

The narrower dimension makes it easier to fit between:

• Stubble
• Rocks
• Roots
• Vegetation
• Uneven ground

while the longer dimension can still provide useful ground coverage.

That's why you'll frequently see compact coils such as 8 x 5.5-inch designs rather than simply an 8-inch round coil.

Larger coils also commonly use elliptical shapes.

The Minelab M15, for example, measures 15 x 12 inches and is designed for greater ground coverage and strong depth potential on suitable open ground.

What Does Double-D Mean?

You'll also regularly see coils described as DD or Double-D.

This refers to the internal winding arrangement rather than the physical size of the coil.

Many modern detectors used for UK coin and artefact hunting use DD coils.

The transmit and receive windings overlap, creating a different detection pattern from other designs such as concentric coils.

DD coils are widely used because they can offer good ground coverage and effective performance across a range of ground conditions.

There are other coil designs, including concentric coils, but that's really a subject worthy of its own guide.

When choosing between accessory coils designed for the same detector platform, the most immediately noticeable difference in everyday detecting will usually be their size and shape.

Which Metal Detector Coil Size Should I Choose?

There isn't one universal answer.

Think about the ground you're going to detect rather than simply looking for the biggest coil available.

If you're detecting...	Consider...
Heavy iron contamination	Small coil
Around old buildings or habitation	Small coil
Woodland and tight spaces	Small coil
Thick or awkward stubble	Small / medium coil
General farmland	Medium coil
Mixed permissions	Medium coil
Open pasture	Medium / large coil
Large cultivated fields	Medium / large coil
Open beaches	Medium / large coil
Areas containing lots of modern rubbish	Small coil
Large clean areas where coverage matters	Large coil
Searching for deeper medium or large targets	Large coil

A Real-World Example: MANTICORE M8 vs M11 vs M15

The Minelab MANTICORE range provides a good real-world example because the same detector can be paired with dramatically different coil sizes.

M8 – 8 x 5.5 Inches

The Minelab M8 is the compact option.

Its smaller elliptical footprint makes it particularly useful for:

• Iron-heavy sites
• Thick stubble
• Woodland
• Gateways
• Busy areas containing closely spaced targets

It isn't the coil we'd choose to quickly cover 50 acres of open pasture.

But put it over an occupation patch littered with iron and the situation changes completely.

M11 – 11 Inches

The M11 is the standard all-rounder.

It's large enough to provide good depth and coverage without becoming excessively cumbersome, while still retaining useful separation for general detecting.

That's exactly why an 11-inch coil is such a common standard size across modern detectors.

M15 – 15 x 12 Inches

The Minelab M15 sits at the opposite end.

Its larger footprint makes it particularly well suited to:

• Open pasture
• Large fields
• Beaches
• Clean ground
• Situations where covering ground efficiently matters

The M8 and M15 aren't really competing with one another.

They're tools for different jobs.

Put us on a huge clean pasture field and we'd probably rather have the M15 than the M8.

Drop us onto a small Roman occupation patch full of iron and we'd probably make the opposite choice.

The site decides which coil is better.

Can Changing Your Coil Help You Find More?

Absolutely.

But perhaps not for the reason people first expect.

The temptation is always to buy a larger coil in search of another inch or two of depth.

Sometimes that can work.

But one of the biggest advantages of owning more than one coil is being able to adapt the detector to the site.

You might search a field with your standard coil and discover a concentrated patch containing pottery, lead and lots of iron.

Instead of simply continuing with the same setup, you could return with a smaller coil and investigate that patch more carefully.

You might then have another permission consisting of acres of relatively clean pasture where a larger coil allows you to cover significantly more ground.

Neither coil is universally better.

They simply solve different problems.

If you're looking to add another coil to your setup, you can browse our full range of metal detector coils to see the options available for different machines.

A better question than:

“Which coil is best?”

is:

“Which coil is best for the ground I'm detecting today?”

Small vs Large Metal Detector Coils: The Bottom Line

If there's one thing to remember, it's that changing coil size always involves some form of trade-off.

Small coils offer precision, manoeuvrability and excellent performance around closely spaced targets.

Medium coils provide a strong balance of depth, coverage and separation for general detecting.

Large coils provide greater ground coverage and can offer additional depth on suitable targets and suitable ground.

But bigger doesn't automatically mean better.

Sometimes the extra find isn't another inch deeper.

It's the tiny hammered coin sitting beside a nail that your smaller coil finally allows you to hear.

And that's exactly why plenty of experienced detectorists eventually end up owning more than one coil.