File sizes tell you how much digital information a file contains or how much storage space it uses. The units begin with bits and bytes, then increase through kilobytes, megabytes, gigabytes, terabytes, petabytes, exabytes, zettabytes and yottabytes.
The short answer is that each decimal unit is 1,000 times larger than the one before it. However, computers and operating systems may also use binary units based on 1,024. This guide explains both systems clearly so you can compare files, storage devices and internet speeds without confusion.
File size units from smallest to largest
The standard order is:
bit < byte < kilobyte < megabyte < gigabyte < terabyte < petabyte < exabyte < zettabyte < yottabyte
| Unit | Symbol | Decimal value | Common use |
|---|---|---|---|
| Bit | b | One binary digit | Internet speed and data transmission |
| Byte | B | 8 bits | A small character or basic data |
| Kilobyte | KB | 1,000 bytes | Small text files and documents |
| Megabyte | MB | 1,000 KB | Photos, audio and documents |
| Gigabyte | GB | 1,000 MB | Apps, videos and device storage |
| Terabyte | TB | 1,000 GB | Hard drives and large backups |
| Petabyte | PB | 1,000 TB | Data centers and large organizations |
| Exabyte | EB | 1,000 PB | Global-scale data measurement |
| Zettabyte | ZB | 1,000 EB | Worldwide data volumes |
| Yottabyte | YB | 1,000 ZB | Extremely large theoretical datasets |
What is a bit?
A bit is the smallest basic unit of digital information. It has one of two values: 0 or 1. The lowercase symbol b represents a bit.
Bits are most commonly used for network speeds. For example, a 100 Mbps internet connection transfers up to 100 megabits per second under ideal conditions. Because 8 bits = 1 byte, the theoretical maximum in megabytes is 100 Mbps ÷ 8 = 12.5 MB/s.
What is a byte?
A byte is a group of eight bits. Its symbol is an uppercase B. File sizes and storage capacity are normally measured in bytes rather than individual bits.
The difference between uppercase and lowercase matters:
- Mb = megabits
- MB = megabytes
- 1 MB = 8 Mb
This explains why a file does not download at the same number shown in an internet plan. A 40 Mbps connection has a theoretical maximum download rate of 40 ÷ 8 = 5 MB/s before network overhead and other real-world factors.
What is a kilobyte?
A kilobyte is a small unit commonly used for text files, simple documents and lightweight images. In the decimal system, 1 KB = 1,000 bytes. In older computer usage, KB is sometimes used informally for 1,024 bytes, but the precise binary term is kibibyte.
A short plain-text document may occupy only a few KB, while a formatted document with fonts and images can be much larger.
What is a megabyte?
A megabyte is used for photos, PDFs, music tracks, mobile data and many software downloads. In decimal notation, 1 MB = 1,000 KB = 1,000,000 bytes.
Actual file sizes vary greatly. A compressed photograph may use several MB, while an uncompressed image with the same dimensions can be much larger. Audio duration, bitrate, image resolution and compression all affect the final size.
What is a gigabyte?
Gigabytes are used for phone storage, computer memory, applications, games and video. In decimal notation, 1 GB = 1,000 MB = 1,000,000,000 bytes.
A device advertised with 128 GB of storage does not provide all 128 GB for personal files. The operating system, installed applications, formatting and system partitions use some of that capacity.
What is a terabyte?
A terabyte is a common unit for hard drives, solid-state drives, backups and large media collections. In decimal notation, 1 TB = 1,000 GB = 1,000,000,000,000 bytes.
The number of files a 1 TB drive can hold depends on their average size. If each photo averages 5 MB, a simple decimal estimate is 1,000,000 MB ÷ 5 MB = about 200,000 photos. Formatting and other storage overhead reduce the usable amount.
What are PB, EB, ZB and YB?
Petabyte
One petabyte equals 1,000 terabytes in decimal measurement. Petabytes are used when discussing large data centers, enterprise backups, research datasets and major online platforms.
Exabyte
One exabyte equals 1,000 petabytes. It is far beyond ordinary personal storage and is useful for describing data across very large networks, industries or countries.
Zettabyte
One zettabyte equals 1,000 exabytes. Zettabytes are used for data volumes at worldwide scale, such as global data creation, storage and network traffic.
Yottabyte
One yottabyte equals 1,000 zettabytes. It represents 1024 bytes in decimal notation. Yottabytes are currently more useful for understanding the scale of future or theoretical data systems than for describing a normal storage device.
KB versus KiB: why 1,000 and 1,024 both appear
Two measurement systems are commonly encountered. Decimal SI units increase by powers of 1,000, while binary IEC units increase by powers of 1,024.
| Decimal unit | Exact value | Binary unit | Exact value |
|---|---|---|---|
| 1 KB | 1,000 bytes | 1 KiB | 1,024 bytes |
| 1 MB | 1,000,000 bytes | 1 MiB | 1,048,576 bytes |
| 1 GB | 1,000,000,000 bytes | 1 GiB | 1,073,741,824 bytes |
| 1 TB | 1,000,000,000,000 bytes | 1 TiB | 1,099,511,627,776 bytes |
The National Institute of Standards and Technology defines 1 MB as 1,000,000 bytes and 1 MiB as 1,048,576 bytes. The International Electrotechnical Commission likewise distinguishes decimal prefixes from binary prefixes.
Storage manufacturers usually advertise drives with decimal units. Some software has historically displayed capacity using binary calculations while labeling the result as GB or TB. This is why a drive can appear smaller in an operating system even though the manufacturer has supplied the advertised number of bytes.
How to convert file sizes
For decimal units, multiply by 1,000 when moving to a smaller unit and divide by 1,000 when moving to a larger unit.
- 5 GB × 1,000 = 5,000 MB
- 2,500 MB ÷ 1,000 = 2.5 GB
- 3 TB × 1,000 = 3,000 GB
For binary units, use 1,024:
- 5 GiB × 1,024 = 5,120 MiB
- 2,048 MiB ÷ 1,024 = 2 GiB
Always confirm whether an app, operating system or specification is using decimal or binary measurement before making an exact comparison.
Typical file sizes in everyday use
File size depends on format, quality, compression and content, so these examples are only rough guides:
- A plain-text note may be a few KB.
- A PDF or office document may range from hundreds of KB to many MB.
- A smartphone photo commonly occupies several MB.
- A compressed music track may use several MB per minute.
- High-resolution video can use hundreds of MB or several GB.
- Modern games and professional applications can require tens or hundreds of GB.
Why file size matters
Understanding storage units helps you choose the right phone or computer, estimate upload and download times, stay within email attachment limits, plan backups and avoid running out of cloud storage.
It also helps with website performance. Large images and videos take longer to transfer. Compressing media, selecting an efficient format and serving appropriately sized images can improve loading speed while preserving acceptable quality.
Frequently asked questions
Which is bigger, MB or GB?
A gigabyte is bigger. In decimal measurement, 1 GB = 1,000 MB.
How many MB are in 1 GB?
In decimal units, 1 GB = 1,000 MB. In binary units, 1 GiB = 1,024 MiB.
How many GB are in 1 TB?
In decimal units, 1 TB = 1,000 GB. In binary units, 1 TiB = 1,024 GiB.
Is 1 KB equal to 1,000 or 1,024 bytes?
Strictly, 1 KB = 1,000 bytes and 1 KiB = 1,024 bytes. Some software and older explanations use KB informally for 1,024 bytes, which causes confusion.
Why is internet speed measured in Mbps instead of MB/s?
Network speeds are normally advertised in bits per second, while file sizes are usually shown in bytes. Divide Mbps by 8 to estimate the maximum MB/s before overhead.
What comes after a yottabyte?
The newer decimal units are ronnabyte and quettabyte. They represent 1027 bytes and 1030 bytes respectively. For the traditional sequence covered here, YB is the largest commonly recognized term.
Final summary
Bytes measure file size, while KB, MB, GB and TB make everyday quantities easier to understand. PB, EB, ZB and YB describe progressively larger datasets. For precise comparisons, remember that decimal units use multiples of 1,000 and binary units use multiples of 1,024 with names such as KiB, MiB and GiB.