What kind of magnet will destroy a hard drive?

Hard drives are a type of non-volatile data storage device commonly found in computers. They store data on one or more spinning platters coated with magnetic material. A read-write head floats just above each platter to read and write data by magnetizing tiny spots on the platter surface. This allows a hard drive to store large amounts of data, from gigabytes to terabytes.

With so much personal and sensitive data stored on hard drives, it’s important to understand how to fully erase or destroy a hard drive when disposing of an old computer. Simply deleting files or formatting a hard drive does not remove data permanently. Powerful magnets can disrupt and wipe hard drive data by overwriting the magnetic spots on the platters. However, magnets must be very strong to have this destructive effect.

How Hard Drives Store Data

Hard drives store data on rapidly rotating platters that are coated with magnetic material. They are circular disks made of glass, aluminum or ceramic. The data itself is stored in microscopic areas of polarity magnetization on the platters.

The surface of each platter is divided into billions of sub-microscopic areas called sectors. Each sector is capable of storing a single bit – either a 0 or 1. Sectors are grouped into tracks which circle around the platters like rings on a tree. There can be tens of thousands of tracks on a single platter.

Data is written and read by an actuator arm with read/write heads on the end that hover just above the surface of the platters. The actuator arm rapidly moves the heads from the center of the platters out to the rim and back to access different tracks. The heads detect the magnetic polarity of each tiny sector as it passes beneath them to read the data.

To write data, the heads apply a magnetic charge to polarize the sectors. A north-pole oriented magnetic field indicates a binary 1, while a south-pole field indicates a 0. This polarization creates a pattern of 1’s and 0’s on the platter to encode the data.

Hard Drive Density

Hard disk drives store data by magnetizing small grains on the disk platter surface. The density of these magnetic grains, known as areal density, determines the drive’s storage capacity. In recent years, growth in HDD areal density has slowed as capacities have increased (https://www.tomshardware.com/news/as-hdds-gain-capacity-their-areal-density-barely-growth).

Areal density is typically measured in gigabits or terabits per square inch. Modern high-capacity HDDs have an areal density around 1 Tbpsi (terabit per square inch). This allows today’s largest HDDs to store up to 20TB of data (https://blog.westerndigital.com/explained-hdd-areal-density/). However, areal density growth has stagnated in the past several years after doubling annually for decades. New innovations will be required to boost HDD density and capacities moving forward (https://www.forbes.com/sites/tomcoughlin/2022/09/18/we-need-a-boost-in-hdd-areal-density/).

Effect of Magnetism

Hard drives store data on platters coated with magnetic material. Data is stored in binary code across millions of tiny magnetic regions called sectors. Each sector has a magnetic polarity, either north or south, to represent 1 or 0. The hard drive head changes the polarity of a sector to write data. To read the data, the head detects the magnetic polarity.

Bringing a magnet near the platters can alter the magnetic polarity of sectors, essentially erasing or corrupting the data. A powerful magnet can randomize the polarity of sectors, rendering them unreadable by the drive head [1]. The strength of the magnetic field determines how much data gets damaged. A weak magnet may only affect sectors in close proximity, while a very powerful magnet can corrupt data across the entire hard drive.

Measuring Magnetic Strength

The strength of a magnet is typically measured in units called Gauss or Tesla. Gauss is the cgs unit for measuring magnetic flux density, while Tesla is the SI unit (1 Tesla = 10,000 Gauss). A Gauss meter is commonly used to measure the magnetic field strength or flux density of a magnet.

Some common measurements for magnet strength in Gauss are:

  • Refrigerator magnets – Around 100 Gauss
  • Standard neodymium magnets – Around 1300 Gauss
  • Strong neodymium magnets – Around 14,000 Gauss or higher
  • MRI machines – Up to 70,000 Gauss

The higher the Gauss rating, the stronger the magnetic field. For comparison, the Earth’s magnetic field measures just 0.5 Gauss. (Source)

Gauss meters can precisely measure the magnetic field strength at various distances from the magnet surface. This allows comparing the relative power of different types and sizes of magnets. The strength drops rapidly as the distance increases. (Source)

Required Strength to Damage a Hard Drive

The strength of a magnetic field is measured in gauss. To damage the integrity of data stored on a hard drive platter, a magnet needs to generate a strong gauss rating of around 10,000 to 20,000 gauss according to industry experts Data Destruction vs Hard Drive Destruction – Degaussing 101. This level of magnetism is strong enough to scramble and rearrange the magnetic orientation of bits on a drive platter, rendering recoverable data useless.

Professional degaussers designed for data destruction generate magnetic fields between 10,000-20,000 gauss according to industry standards. This meets guidelines set by organizations like the National Institute of Standards and Technology (NIST) for reliably destroying sensitive data stored on hard drives. Using a degausser certified to these standards ensures the magnetic media is completely sanitized and data is unrecoverable according to 4 Interesting Facts About Degaussing a Hard Drive.

Types of Strong Magnets

There are several types of magnets capable of generating a strong enough magnetic field to damage or destroy a hard drive. The most powerful options include:

Neodymium Magnets

Neodymium magnets, which are made from an alloy of neodymium, iron and boron, are the strongest permanent magnets available commercially. They can be 10-15 times stronger than standard ceramic or ferrite magnets. According to Amazon, they offer extremely strong magnetic properties and “can destroy credit cards, laptops, tablets and other magnetic media”[1]. The strength of neodymium magnets is measured in grades – N35 to N52 – with higher grades indicating a stronger magnetic field. An N52 grade neodymium magnet can have a pull force over 1,200 gauss.


Electromagnets generate magnetic fields through electricity and can be designed to produce extremely powerful magnetic forces. They consist of a core made of ferromagnetic material like iron that is wrapped in conducting wire. When electric current passes through the wire, it creates a magnetic field significantly stronger than a permanent magnet. The strength depends on the number of wire coils and amount of electric current. Custom electromagnets can be built to generate fields exceeding 20,000 gauss, easily enough to damage magnetic storage on a hard drive.[2]

Using Magnets Safely

When using magnets to destroy hard drives, it is important to exercise caution. Strong magnets pose risks if not handled properly.

Safety precautions when using magnets include:

  • Wear protective gloves when handling strong magnets. The magnetic force can cause pinching injuries.
  • Store magnets securely away from sensitive objects. Magnets can damage items like credit cards, watches, and other electronics.
  • Keep a safe distance between magnets. Allowing magnets to snap together can lead to fractures and chips.
  • Follow manufacturer guidelines for safe use and care.

In terms of data security best practices, physically destroying hard drives with magnets is an extreme measure with risks. While it can make data recovery difficult, it does not guarantee permanent data destruction. For proper hard drive sanitization, standards like NIST 800-88 recommend multi-pass software wiping or physical shredding and disintegration.

Rather than using magnets, more reliable methods of hard drive destruction for data security include:

  • Using wiping software to overwrite the drive multiple times
  • Physically shredding or disintegrating the platters
  • Degaussing the drive using powerful magnetic force
  • Hiring certified data destruction services

While magnets can damage drives, best practices involve more thorough and foolproof means of destruction. Handling magnets safely and seeking more reliable methods protects both user safety and sensitive data.

Alternative Data Destruction Methods

Besides using magnets, there are other ways to destroy a hard drive and the data stored on it. Some common methods include:

Physical Destruction

Physically destroying the hard drive is an effective way to make the data unrecoverable. Methods like smashing, crushing, shredding or drilling holes can damage the platters and circuitry beyond repair (Source). However, specialized equipment may be required for physical destruction, and safety precautions need to be taken.

Data Wiping Software

Data wiping or disk wiping software can overwrite the data on a hard drive multiple times with random data to make the original data inaccessible (Source). This method does not damage the physical drive. However, advanced forensic data recovery methods may still be able to recover some data.


Degaussing exposes the hard drive to a powerful magnetic field that realigns the magnetic domains and erases the data (Source). Handheld degaussing wands are available, but may not generate a strong enough magnetic field for modern high-density drives. Industrial degausser machines are more effective but expensive.


In this article, we discussed how hard drives store data through magnetization of platters. The higher density of modern drives means they are more susceptible to data loss from external magnetism. Though measurements like gauss and oersted quantify magnetic strength, even simple household magnets can damage drives if brought into close contact.

Powerful magnets like neodymium rare earth can quickly degauss a hard drive from inches away, destroying vast amounts of data. Accidental exposure is a real risk, so magnets should always be handled carefully around sensitive electronics.

While magnets provide a quick way to damage drives, more thorough methods like disk wiping software or physical destruction ensure complete, irrecoverable data loss. The dangers magnets pose to hard drives should not be underestimated.

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