Bits, bytes and prefixes
Every file, photo and disk is measured in bytes, each made of 8 bits. Prefixes then scale the byte up: kilo, mega, giga, tera and peta. The catch is that computers work in powers of two, and for decades the industry used kilo for 1,024 as well as 1,000. The two meanings drift further apart at each step, from 2.4% for kilo to almost 10% for tera, which is where most confusion comes from.
How to use this converter
Type a size in any field and every other unit updates as you type. Use the decimal units (kB, MB, GB, TB) for drive labels, mobile data plans and macOS. Use the binary ones (KiB, MiB, GiB, TiB) for RAM, Linux tools and the sizes Windows displays. Common pairs below each have a page with the formula, an example and a chart.
Key equivalents
- 1 byte = 8 bits
- 1 kB = 1,000 bytes, and 1 KiB = 1,024 bytes
- 1 GB = 1,000 MB = 0.9313 GiB
- 1 GiB = 1,024 MiB = 1.0737 GB
- 1 TB = 1,000 GB = 0.9095 TiB ≈ 931 GiB
Decimal and binary units
In 1998 the International Electrotechnical Commission created separate names for the binary values: kibibyte, mebibyte, gibibyte and tebibyte, written KiB, MiB, GiB and TiB. The SI prefixes kept their decimal meaning. Drive manufacturers, network equipment and macOS follow the decimal convention. RAM makers and Windows still use the binary values, but Windows labels them KB, MB and GB, so a disk can look smaller than advertised. This converter keeps both families apart so that you always know which one you are reading.
Estimating what fits
Sizes vary with quality settings, but rough figures help. A smartphone photo takes 2 to 5 MB, a minute of 4K video around 170 to 400 MB, a song in MP3 about 3 to 5 MB, and an hour of HD streaming 1.5 to 3 GB. Leave some free space on any drive: file systems and operating systems need room to work.
Data storage units compared
| Unit | Symbol | In bytes |
|---|---|---|
| Bit | bit | 0.125 |
| Byte | B | 1 |
| Kilobyte | kB | 1,000 |
| Megabyte | MB | 1,000,000 |
| Gigabyte | GB | 1,000,000,000 |
| Terabyte | TB | 1,000,000,000,000 |
| Petabyte | PB | 1 × 10¹⁵ |
| Kibibyte | KiB | 1,024 |
| Mebibyte | MiB | 1,048,576 |
| Gibibyte | GiB | 1,073,741,824 |
| Tebibyte | TiB | 1,099,511,627,776 |
The units in detail
What is a bit?
The bit, short for binary digit, is the smallest unit of information: a single 0 or 1. Storage is counted in bytes, but network speeds and memory chip densities are usually counted in bits.
What is a byte?
The byte is a group of 8 bits, enough to store one character of plain English text. It is the basic unit of file sizes and memory. Its symbol is a capital B, while a lowercase b means bit.
What is a kilobyte?
The kilobyte, in the decimal SI sense, is 1,000 bytes. A short plain-text email weighs a few kB. Some software still uses KB to mean 1,024 bytes; the precise name for that is the kibibyte, KiB.
What is a megabyte?
The megabyte is one million bytes. A phone photo takes 2 to 5 MB and a minute of MP3 music about 1 MB. Email attachments are often limited to 20 or 25 MB.
What is a gigabyte?
The gigabyte is one billion bytes, the usual unit for phone storage, RAM and mobile data plans. An hour of HD streaming video uses roughly 1.5 to 3 GB depending on the service and quality.
What is a terabyte?
The terabyte is one trillion bytes, or 1,000 GB. Hard drives, SSDs and cloud backups are sold in TB. A 1 TB drive holds about 250,000 photos of 4 MB.
What is a petabyte?
The petabyte is 1,000 terabytes, or 10¹⁵ bytes. It measures data centers, scientific archives and the libraries of streaming services rather than personal devices.
What is a kibibyte?
The kibibyte is 1,024 bytes, or 2¹⁰. The IEC introduced the binary prefixes kibi, mebi, gibi and tebi in 1998 to end the confusion between 1,000 and 1,024. Memory page sizes, such as 4 KiB, are naturally binary.
What is a mebibyte?
The mebibyte is 1,048,576 bytes, or 1,024 KiB. It is about 4.9% larger than a megabyte. Linux tools and many programs labeled MB actually display MiB.
What is a gibibyte?
The gibibyte is 1,073,741,824 bytes, or 1,024 MiB, about 7.4% larger than a gigabyte. RAM modules are binary: a stick sold as 16 GB actually holds 16 GiB. Windows also shows disk sizes in GiB while labeling them GB.
What is a tebibyte?
The tebibyte is 2⁴⁰ bytes, about 1.0995 terabytes. The gap between binary and decimal grows with each prefix and reaches almost 10% at this scale, which is why a 4 TB drive shows about 3.64 TB in Windows.