How is hard drive size measured?

A hard drive is a data storage device used in computers and other devices like smartphones, tablets, and game consoles. The main purpose of a hard drive is to store digital information persistently, including the operating system, software applications, files, and media like photos, music, and videos (, 2023). Hard drives allow users to retrieve data quickly and to store large amounts of data, beyond what could fit in the computer’s main memory (TechTerms, 2023). They provide non-volatile storage, meaning the data remains even when the device is powered off.

Unit of Measure

Hard drive size is measured in bytes (What is byte? A definition from A byte is a unit of digital information that most commonly consists of eight bits. It is the fundamental unit of information used to quantify data size and storage capacity in computing (What is a Byte?).

Originally, a byte represented the smallest addressable unit of memory in early computer systems. Over time, the size of a byte became standardized based on factors like the emergence of networking technology and disk drives (What is a Byte? | Overview & Size). Today, a byte is universally accepted as consisting of eight bits, which allows it to represent 256 possible values.

Hard drive manufacturers leverage bytes as a standard unit to measure and market the data storage capacity of their drives. Consumers can easily compare products and understand how much data they can expect to store based on the byte specification.


A kilobyte (KB) is 1024 bytes 1. The prefix “kilo” means 1000, however in computer storage a kilobyte is actually equal to 210 or 1024 bytes. This is because computer storage uses binary digits (bits) rather than decimal digits, and 210 is 1024 in base 10. So when referring to computer memory or storage, a kilobyte represents 1024 bytes, not 1000 bytes.


A megabyte (MB) is equal to 1,024 kilobytes or 1,048,576 bytes (Megabyte Definition & Meaning). One megabyte contains about 1 million bytes of information. The prefix “mega” comes from the Greek word meaning “great” and is commonly used in units of measurement to denote multiplication by a factor of 1 million (106). In computing, megabytes are used to measure hard drive size, file size, RAM memory, and data transfer speeds.

For most practical purposes, 1 megabyte can hold approximately:

  • 250 pages of plain text
  • A 3.5 minute song encoded in MP3 format
  • A high resolution photograph

Megabytes became more widely used in computing during the 1990s as file sizes and storage capacities grew. For example, many software applications and digital media files today range from 1-500+ MB in size. Understanding megabytes helps conceptualize the difference between kilobytes and gigabytes when looking at technical specifications.


A gigabyte (GB) is equal to 1024 megabytes (MB) or 1,073,741,824 bytes. Gigabytes are commonly used to measure the storage capacity of computer hard drives and other data storage devices. For example, a 500 GB hard drive can store 500 gigabytes worth of data, which equates to 524,288,000,000 bytes or 500 x 1024 MB.

According to the Merriam-Webster dictionary, a gigabyte is defined as “1024 megabytes or 1,073,741,824 bytes; also : one billion bytes.” [1] The ‘giga’ prefix stands for ‘billion’ indicating the large storage capacity that gigabytes represent. While some storage manufacturers use ‘gigabyte’ loosely to mean ‘one billion bytes’, the standard definition in computing and technology equates it to 2^30 or 1024^3 bytes.



A terabyte is a unit of digital data storage equal to 1 trillion bytes or 1024 gigabytes. According to the Merriam-Webster dictionary, the meaning of terabyte is: “1024 gigabytes or 1099511627776 bytes; also: one trillion bytes.”1 In computing and digital storage, a terabyte is a common unit used to measure large quantities of data.

To understand terabytes, it helps to first understand the relationship between bytes, kilobytes, megabytes, and gigabytes. A kilobyte is approximately 1000 bytes, a megabyte is approximately 1000 kilobytes, a gigabyte is approximately 1000 megabytes, and a terabyte is approximately 1000 gigabytes. So a single terabyte contains over 1 trillion individual bytes of data.

With the increasing size of digital media files and storage demand from users, terabyte-sized drives are becoming more common among consumer devices. Many external hard drives today have capacities of 1 terabyte or higher. Terabyte-capacity drives can hold enormous quantities of documents, photos, videos, software, games, and other files.


A petabyte is equal to 1024 terabytes (PETABYTE Definition & Usage Examples). That means a single petabyte is over 1 million gigabytes. To put it in perspective, 5 petabytes could store the entire written works of mankind from the beginning of recorded history in all languages (Petabyte – Wasabi).


An exabyte is a unit of digital information storage that is equal to approximately one quintillion (1,000,000,000,000,000,000) bytes. More specifically, one exabyte is equal to 1024 petabytes, according to Wasabi.

To put the size of an exabyte into perspective, it would take over 500 billion floppy disks to store just one exabyte of data. Some real world examples of exabyte scale data include the total volume of data produced globally each day across the internet, as well as the total data stored in the world’s largest data centers like those operated by Google, Facebook, and Amazon.

While exabytes represent an incredibly large amount of digital information today, even larger units like zettabytes and yottabytes have been proposed to account for future growth in data driven by trends like big data analytics, IoT devices, and AI/machine learning.


A zettabyte is equal to 1,000,000,000,000,000,000,000 bytes or 1024 exabytes. It’s an enormous unit of digital information storage. To put the size of a zettabyte into perspective:

  • All the data on the internet was estimated at around 2 zettabytes in 2019.
  • Facebook processes over 10 billion photos per day. At 500KB per photo, storing one day’s worth of Facebook photos would take around 5 zettabytes.
  • The human brain can store 2.5 petabytes of information. So 1 zettabyte would have the storage capacity of over 400,000 human brains.

As technology advances and more data is created and stored digitally, zettabytes will likely become a more commonly used unit of measurement for massive data storage needs. Some experts predict we may reach the zettabyte era by 2025, when global data storage surpasses 2 zettabytes annually.


A yottabyte is the largest unit used to measure data capacity. One yottabyte is equal to 1,000,000,000,000,000,000,000,000 bytes, or 1024 zettabytes

To put the massive size of a yottabyte into perspective, according to Merriam-Webster, if every person in the world made a phone call that lasted one hour every hour, it would take over 90 yottabytes to store the phone call data for one year

As of 2023, no storage device has yet reached the yottabyte capacity. Theoretical estimates predict yottabyte storage may become achievable between 2030 and 2040 as technology continues advancing.