Data Size Converter (Bytes, KB, MB, GB, TB, KiB, MiB, GiB)
Convert between bits, bytes, kilobytes, megabytes, gigabytes and terabytes in both the decimal (SI, 1 GB = 10⁹ bytes) and binary (IEC, 1 GiB = 2³⁰ bytes) systems, and see why a 1 TB drive shows up as 931 GB.
Last updated: October 2026
Converted size
1,000 MB
Formula below · 3 sources (physics.nist.gov, NIST, bipm.org) · Updated Oct 2026
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About this calculator
A byte is 8 bits. Beyond that there are two competing systems of prefixes. The decimal (SI) prefixes, used by disk manufacturers, network speeds, download pages and the file-size display on macOS, go up by 1,000: 1 KB = 1,000 bytes, 1 MB = 10⁶ bytes, 1 GB = 10⁹ bytes, 1 TB = 10¹² bytes. The binary (IEC) prefixes, used by memory sizes and by Windows Explorer (which labels them KB, MB, GB although it computes with 1,024), go up by 1,024 = 2¹⁰: 1 KiB = 1,024 bytes, 1 MiB = 1,048,576 bytes, 1 GiB = 1,073,741,824 bytes, 1 TiB = 1,099,511,627,776 bytes. NIST and the IEC standardised the kibi/mebi/gibi names in 1998 precisely to end the ambiguity.
The gap grows with each step: KiB is 2.4% larger than KB, MiB 4.9% larger than MB, GiB 7.4% larger than GB and TiB 10% larger than TB. That is the whole explanation for the 1 TB drive that Windows reports as 931 GB: 10¹² bytes ÷ 2³⁰ = 931.3 GiB, and Windows writes GB where it means GiB.
The converter turns the input into bytes using the exact factor of its unit, then divides by the factor of the target unit. Bit units (Kb, Mb, Gb) are one eighth of the byte units with the same prefix and always decimal here, matching how network and streaming rates are quoted; a 100 Mb file is 12.5 MB. Results are shown to six significant figures.
How to use
Example (the defaults): 1 GB to MB. 1 GB = 10⁹ bytes and 1 MB = 10⁶ bytes, so 1 GB = 1,000 MB. The tiles show the same amount as 1,000,000,000 bytes, 8,000,000,000 bits and 0.9313 GiB. Why a 1 TB drive shows 931 GB: set 1 TB to GiB. 10¹² ÷ 1,073,741,824 = 931.323 GiB. Nothing is missing; the operating system is counting in binary units. RAM the other way: 16 GiB of memory is 16 × 1,073,741,824 = 17,179,869,184 bytes = 17.18 GB. A 4.7 GB DVD holds 4,700,000,000 bytes = 4.38 GiB, so a 4.5 GiB file does not fit on it.
Frequently asked questions
Is 1 GB 1,000 MB or 1,024 MB?
By the SI definition that NIST and the IEC adopted, 1 GB is 1,000 MB (10⁹ bytes) and 1,024 MiB is a gibibyte, 1 GiB = 1,073,741,824 bytes. The confusion comes from software that uses 1,024 but prints GB: Windows reports a 500 GB (5 × 10¹¹ byte) disk as 465 GB because it is really showing GiB. When a figure matters, say which system you mean; this converter lists both so you can pick exactly the unit your source uses.
How many bytes are in a kilobyte, megabyte, gigabyte and terabyte?
Decimal: 1 KB = 1,000 bytes, 1 MB = 1,000,000, 1 GB = 1,000,000,000, 1 TB = 1,000,000,000,000. Binary: 1 KiB = 1,024, 1 MiB = 1,048,576, 1 GiB = 1,073,741,824, 1 TiB = 1,099,511,627,776. Each binary unit is 1,024 of the previous one, each decimal unit 1,000. A petabyte continues the pattern: 10¹⁵ bytes (PB) or 2⁵⁰ bytes (PiB).
What is the difference between a megabit (Mb) and a megabyte (MB)?
A byte is 8 bits, so 1 MB = 8 Mb. Internet speeds are quoted in megabits per second (Mbps) while file sizes are in megabytes, so a 100 Mbps connection moves at most 12.5 MB per second. Lowercase b means bits, uppercase B means bytes; getting this wrong makes a download estimate eight times too optimistic. The bit units here are decimal (1 Mb = 1,000,000 bits), as in networking.
Why does my phone or SSD show less space than advertised?
Two reasons. The label uses decimal gigabytes while the device often counts in binary (a 256 GB phone is 238 GiB before anything is installed). On top of that, the operating system, recovery partition and file-system structures occupy space, which can take another few gigabytes. The unit effect is exactly predictable with this converter; the system overhead varies by device.
How precise is the conversion?
The factors are exact (powers of 10 and powers of 2), so the only rounding is in the display, which shows six significant figures; 1 GB in GiB is 0.931323 and 1 TiB in GB is 1,099.51. The byte and bit tiles are shown as whole numbers. For amounts beyond about 9 × 10¹⁵ bytes the floating-point arithmetic itself starts rounding, which is well past a petabyte.
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