Data Storage Converter

How it works

Every size is first turned into bytes (a bit is one eighth of a byte), then divided by the size of the unit you are converting to. Only the two factors matter: what one of the source unit is in bytes, and what one of the target unit is in bytes.

There are two families of prefix, and they are not interchangeable. The decimal (SI) prefixes kilo, mega, giga and tera mean 1,000, 1,000,000, 10⁹ and 10¹² bytes: 1 kB = 1,000 B. The binary prefixes kibi, mebi, gibi and tebi, standardised in IEC 80000-13, mean 1,024, 1,024², 1,024³ and 1,024⁴ bytes: 1 KiB = 1,024 B. The gap grows with each step: KiB is 2.4% bigger than kB, MiB 4.9% bigger than MB, GiB 7.4% bigger than GB and TiB 10% bigger than TB.

Drive makers label capacity in decimal units, while Windows reports sizes in binary units but labels them KB, MB, GB and TB. That is why a drive sold as 1 TB (10¹² bytes) shows as 931 GB: it holds 931.32 GiB. Nothing is missing; the two numbers are the same quantity in different units.

Formula

bytes       = size × bytes per source unit
converted   = bytes ÷ bytes per target unit
1 byte = 8 bits
decimal:  1 kB = 10³ B,  1 MB = 10⁶ B,  1 GB = 10⁹ B,  1 TB = 10¹² B      (SI prefixes)
binary:   1 KiB = 2¹⁰ B, 1 MiB = 2²⁰ B, 1 GiB = 2³⁰ B, 1 TiB = 2⁴⁰ B      (IEC 80000-13)

Example

A 1 TB drive, the default, is 1 × 10¹² = 1,000,000,000,000 bytes. Divided by 1,073,741,824 bytes per GiB that is 931.322575 GiB, which is the "931 GB" an operating system that counts in binary units reports. It is also 8,000,000,000,000 bits and 0.909495 TiB.

A 4 GiB memory module is 4 × 2³⁰ = 4,294,967,296 bytes, or 4.294967 GB in decimal units. Going the other way, a 500 GB drive is 500 × 10⁹ ÷ 2³⁰ = 465.661 GiB.

Assumptions and limitations

• Decimal prefixes follow the SI (kB = 1,000 bytes) and binary prefixes follow IEC 80000-13 (KiB = 1,024 bytes). Software that writes "GB" but counts in units of 1,073,741,824 bytes is using GiB; read its figures from the binary rows of the table.
• A byte is eight bits. Network speeds are usually quoted in bits per second (Mbps), file sizes in bytes; this converter handles the unit, not the per-second part.
• Only decimal multiples up to tera and binary multiples up to tebi are listed. Petabytes and larger can be entered as thousands of TB.
• The table rounds to six decimal places, so a size that is tiny in a large unit (one byte in TiB) displays as 0.

Frequently asked questions