Convert between bytes, kilobytes, megabytes, gigabytes and terabytes — choose SI (decimal) or binary units.

What this tool does

This converter moves between bytes, kilobytes, megabytes, gigabytes and terabytes in either SI (decimal) or binary (IEC) notation. Pick your from-unit, your to-unit, choose the unit system, and the result updates instantly in your browser.

The key question is whether "kilobyte" means 1,000 bytes or 1,024 bytes. Both definitions are in active use, and the difference becomes significant at larger scales — a 1 TB hard drive holds roughly 9% fewer bytes than 1 TiB.

SI (decimal) vs binary (IEC) units

SI prefixes (decimal)

1 KB = 1,000 B · 1 MB = 1,000 KB · 1 GB = 1,000 MB · 1 TB = 1,000 GB

IEC prefixes (binary)

1 KiB = 1,024 B · 1 MiB = 1,024 KiB · 1 GiB = 1,024 MiB · 1 TiB = 1,024 GiB

SI (International System of Units) prefixes — kilo, mega, giga, tera — have always meant powers of 10. The IEC formalised the binary equivalents in 1998 with new names: kibibyte (KiB), mebibyte (MiB), gibibyte (GiB), tebibyte (TiB), where 1 KiB = 2¹⁰ = 1,024 bytes.

Why the confusion exists

Before the IEC standard, the computing industry routinely used "KB" to mean 1,024 bytes because RAM and processor caches are addressed in powers of two. Hard-drive and flash manufacturers, by contrast, adopted the SI convention (1 KB = 1,000 B) because it makes their capacity figures look larger. The result: an operating system may report a 500 GB drive as 465 GiB (i.e. 465 binary gigabytes) and the user wonders where 35 GB went.

Windows historically labelled binary units with SI names ("MB", "GB"), while macOS switched to SI units in macOS 10.6 Snow Leopard (2009), so the same file may appear as a different size on each OS.

Worked example

Take 1 GB. In SI mode:

1 GB × 1,000 = 1,000 MB

Each step up the SI scale is a factor of 1,000. To convert from a larger unit to a smaller one, multiply; to go the other way, divide.

In binary mode, 1 GiB = 1,024 MiB rather than 1,000 MiB, so 1 GiB = 1,073,741,824 bytes.

Common uses

Storage shopping: comparing drive capacities quoted in SI (manufacturers) with what your OS reports in binary.
Network speeds: ISPs quote speeds in Mbps (megabits per second, SI). To find how long a 4 GB file takes to download, divide the file size in megabits by your speed in Mbps.
Cloud and container limits: Docker memory limits, AWS instance storage, and database size quotas may use either convention.
File-transfer estimates: converting a folder size in GiB to bytes to verify it fits on removable media.

Frequently asked

Is a gigabyte 1,000 MB or 1,024 MB?

In SI it is exactly 1,000 MB. In binary (IEC) it is 1 GiB = 1,024 MiB. Hard drives are sold in SI; your OS may display the same drive in either unit — hence the apparent "missing" space.

What does Windows use?

Windows File Explorer labels sizes in binary units (GiB, MiB) but writes "GB" and "MB". So a 1.00 GB file in Windows means 1,073,741,824 bytes — the binary definition despite the SI label.

What does macOS use?

Since macOS 10.6 (2009), Finder uses SI units: 1 GB = 1,000,000,000 bytes. A file that macOS calls 1 GB is therefore about 6.9% smaller than one Windows calls 1 GB.

How many bytes is 1 TB?

SI: 1 TB = 1,000,000,000,000 bytes exactly. Binary: 1 TiB = 1,099,511,627,776 bytes (2⁴⁰). The difference is about 9.95%.

Data Storage Converter