Data Size Converter: KB vs KiB, MB, GB and TB

The data size converter changes a value between eleven units of digital data: bit, byte (B), kilobyte (KB), megabyte (MB), gigabyte (GB), terabyte (TB), petabyte (PB), kibibyte (KiB), mebibyte (MiB), gibibyte (GiB) and tebibyte (TiB). Type on either side; the All Units list repeats the quantity in every unit.

Updated 2026-09-30Reviewed by CalcX Editorial Team5 sources5 min read

What the data size converter does

Two families share the list: KB, MB, GB, TB and PB step by powers of ten (1 KB = 1,000 B), while KiB, MiB, GiB and TiB step by powers of two (1 KiB = 1,024 B). The byte is exactly 8 bits in both: 100 Mbit is 12.5 MB. A rate times a duration is a size — arithmetic on the standard calculator, durations on the time converter, speeds on the speed converter.

How to use it

Choose the two units.The page opens with bit left and byte right, so 1 reads 0.125 B.
Type the value.The other card converts as you type: 1 KB reads 1,000 B, 1 KiB reads 1,024 B.
Use an expression when it helps.In the KB card, 1000+24 shows the hint = 1,024 and the byte card reads 1,024,000 B; Enter or = settles the input to 1024.
Swap, or pick from the list.The arrow button exchanges the units and carries the value shown; clicking a row moves that unit to the active side.

Worked examples

One byte, one bit. 1 B is exactly 8 bit, and a 100 Mbit/s line moves 12.5 MB (12,500,000 B, or 12,207.03125 KiB) each second.

The two ladders. Decimal: 1 KB = 1,000 B, 1 MB = 1,000 KB, 1 GB = 1,000,000,000 B, 1 TB = 1,000 GB, 1 PB = 1,000 TB. Binary: 1 KiB = 1,024 B, 1 MiB = 1,048,576 B, 1 GiB = 1,073,741,824 B, 1 TiB = 1,024 GiB.

The gap. 1 GiB = 1.073741824 GB, 7.3741824% more than a decimal gigabyte; read the other way, 1 GB = 0.9313225746 GiB, about 6.9% less. It widens at the next rung: 1 TiB = 1.0995116278 TB, and 1 TB = 0.9094947018 TiB.

The drive in the operating system. A 500 GB drive holds 465.661287308 GiB, a 1 TB drive 931.322574615 GiB, a 256 GB SSD 238.418579102 GiB. Windows prints 465 GB and 931 GB — the same bytes divided by 2³⁰. Memory is different: 16 GiB is 17,179,869,184 B, or 17.179869184 GB.

Where the factors come from

The bit is the base unit of information; the byte is 8 bits. Werner Buchholz coined “byte” in June 1956 at IBM, respelling “bite” so it would not be read as “bit”. IEC 80000-13 codified the 8-bit byte and its B symbol; the octet is the same 8 bits.

Decimal prefixes come from the SI: k = 10³, M = 10⁶, G = 10⁹, T = 10¹², P = 10¹⁵, with kilo keeping its lowercase k. The IEC binary prefixes Ki, Mi, Gi and Ti, adopted in December 1998 and now in IEC 80000-13, mean 2¹⁰ to 2⁴⁰: 1 GiB = 1,073,741,824 B and 1 GB = 1,000,000,000 B exactly. Storage makers follow the SI series; RAM and Windows keep the binary habit.

Reading results and limits

Display rule.: Results carry 12 significant digits with at most 10 decimal places, thousands separators and 0 for zero.
Ten-decimal cap and exponents.: The ten-decimal cap decides some readouts: exact 1 GB in GiB is 0.9313225746154785…, printed as 0.9313225746, and 1 TB in TiB prints as 0.9094947018. Outside 10⁻¹⁰–10¹⁵ results switch to exponential form with six decimals: 1 byte in TiB reads 9.094947e-13 TiB, while 1 bit in GiB, just above the cut, reads 0.0000000001 GiB.
Stored values and swaps.: Twelve significant digits round large exact integers too: 1 TiB is exactly 1,099,511,627,776 B, displayed as 1,099,511,627,780 B. A swap carries the displayed value: 1 GB → GiB shows 0.9313225746, and swapping back leaves the byte row at 999,999,999.983 B.
Sizes only.: It does not convert rates or times: 100 Mbit/s is a rate on the speed converter, and durations on the time converter.

Representative readouts:

Input (left card)	Row	Readout
1 GB	Gibibyte	0.9313225746 GiB
1 GiB	Gigabyte	1.073741824 GB
1 bit	Gigabyte	0.0000000001 GB
1 PB	Bit	8.000000e+15 bit
1 byte	Tebibyte	9.094947e-13 TiB

Common mistakes

KB is not KiB. 1 KB is 1,000 B, 1 KiB is 1,024 B — 2.4% more; the gap grows to 7.4% at giga and 10.0% at tera. Reading a “512 GB” drive as 512 GiB is the classic 7% shortfall.
Neither drive number is fake. A 1 TB drive holds 1,000,000,000,000 B — also 931.322574615 GiB. The manufacturer counts decimal, the operating system divides by 2³⁰ under the GB label.
One factor per step. KB → KiB multiplies by 1.024, but GB → GiB divides by 1.073741824 — not 1.024.
Bits and bytes in rates. A 100 Mbit/s link moves 12.5 MB/s, not 100 MB/s: network rates use decimal prefixes, and a byte is 8 bits.
Typing a rounded readout back. Re-entering 0.9313225746 GiB instead of 1 GB gives 999,999,999.983 B. Keep the byte count when the last digits matter.

Where it is used

Drive capacity. A 500 GB drive holds 465.661287308 GiB, the number an operating system prints as 465 GB because it divides by 2³⁰.
Network throughput. A 100 Mbit/s line moves 12.5 MB each second, so rates and byte counts line up across decimal and binary units.
Memory sizes. RAM in GiB against bytes or decimal gigabytes: 16 GiB is 17,179,869,184 B, or 17.179869184 GB.

Sources

IEC, IEC 80000-13:2025 — Quantities and units, Part 13: Information science and technology — with prefixes for binary multiples. webstore.iec.ch （访问日期：2026-09-30）
BIPM, The International System of Units (SI Brochure), 9th edition — the decimal prefixes k, M, G, T and P as powers of 10. bipm.org （访问日期：2026-09-30）
NIST, Prefixes for binary multiples — 1 KiB = 1,024 B, 1 GiB = 1,073,741,824 B, 1 GB = 1,000,000,000 B. nist.gov （访问日期：2026-09-30）
Wikipedia, Byte — the 8-bit byte, Buchholz's June 1956 coinage and the B symbol. en.wikipedia.org （访问日期：2026-09-30）
Wikipedia, Binary prefix — the 1998–99 IEC adoption, the +2.4%, +7.4% and +10% gaps, and Windows reporting binary values under GB labels. en.wikipedia.org （访问日期：2026-09-30）