How the KB/MB/GB Converter works
Storage sizes are written with the same letters but can mean two different amounts. In the decimal (SI) system used by drive manufacturers, network speeds and macOS, 1 KB is 1,000 bytes, 1 MB is 1,000 KB, 1 GB is 1,000 MB and 1 TB is 1,000 GB. In the binary system used by Windows, RAM sizes and many command-line tools, each step is 1,024. The IEC gave the binary units their own names in 1998: kibibyte (KiB), mebibyte (MiB), gibibyte (GiB) and tebibyte (TiB).
The gap grows with each step: a KiB is 2.4% larger than a KB, a MiB 4.86% larger than an MB, a GiB 7.37% larger than a GB and a TiB 9.95% larger than a TB. That is why a drive sold as 1 TB (1,000,000,000,000 bytes) shows as about 931 GB in Windows: Windows divides by 1024³ (giving 931.32 GiB) but labels the result GB. No capacity is missing; the same number of bytes is being counted in bigger units.
The converter works out the exact number of bytes with decimal arithmetic and then divides by the exact size of each unit, so whole numbers are never rounded.
How to use the KB/MB/GB Converter
- In the first section, type a size and choose its unit, for example 500 and GB.
- Read the side-by-side table: each row shows the size in a decimal unit (1000-based) and the matching binary unit (1024-based). Change Precision to show more or fewer digits.
- In the second section, enter the capacity printed on a drive or memory card and choose MB, GB or TB.
- Compare the size in binary units, which is the number Windows shows, with the advertised decimal size and the percentage difference.
- Select Copy next to a value to copy it.
Example
An advertised 1 TB drive:
Advertised capacity in bytes 1,000,000,000,000 bytes
Size in binary units 931.32 GiB (Windows shows this number labelled GB)
Size in decimal units 1,000 GB
How much smaller the binary number looks 6.87% (68.68 GiB)And 500 GB in the side-by-side table:
Prefix Decimal (1000-based) Binary (1024-based)
Kilo 500,000,000 KB 488,281,250 KiB
Mega 500,000 MB 476,837 MiB
Giga 500 GB 465.661 GiB
Tera 0.5 TB 0.454747 TiBCommon use cases
- Understanding why a new 1 TB drive shows as 931 GB in Windows.
- Converting cloud storage or hosting quotas between MB and GB.
- Checking whether a memory, disk or volume size in a configuration file uses 1000 or 1024.
- Explaining the difference between GB and GiB to colleagues or customers.
Common errors and how to fix them
- The converted size does not match my file manager
- Windows reports binary sizes but labels them KB and MB, while drive manufacturers and most Linux tools use decimal units. Read the decimal and binary results side by side and compare like with like.
- A finite number is required
- Enter a plain number. Values with thousands separators, a unit typed into the box, or an arithmetic expression are not parsed.
- An upload is rejected even though the size looks within the limit
- Services differ over which unit a limit means. When a limit says 25 MB, check whether that is 25,000,000 or 26,214,400 bytes, and leave headroom for encoding overhead: Base64 attachments grow by roughly a third.
Frequently asked questions
Is 1 GB 1,000 MB or 1,024 MB?
Both are in use. In the SI (decimal) system 1 GB is 1,000 MB, which is how drive makers, network speeds and macOS count. In the binary system 1 GiB is 1,024 MiB, which is how Windows and RAM sizes count, although Windows still writes GB.
Why does my 1 TB drive show only 931 GB?
The drive holds 1,000,000,000,000 bytes, as advertised. Windows divides that by 1,073,741,824 (1024³) and gets 931.32, which it labels GB. Nothing is missing; the same bytes are measured in a larger unit. A formatted drive shows a little less again because the partition table and file system use some space.
How much larger is each binary unit?
A KiB is 2.4% larger than a KB, a MiB 4.86% larger than an MB, a GiB 7.37% larger than a GB and a TiB 9.95% larger than a TB, because the 2.4% difference compounds at each step.
Does macOS show the advertised size?
Since Mac OS X 10.6, macOS reports storage in decimal units, so a 1 TB drive is shown as about 1 TB before formatting overhead. iOS does the same.
Are the results rounded?
Byte counts are calculated exactly, and whole-number parts are always shown in full. Fractional parts are rounded to the precision you choose in the first section; the drive calculator rounds to two decimal places like most operating systems.