Data Storage Converter
Exact bits and bytes in decimal and binary units — and why 1 TB shows as 931 GB.
Drives, memory cards, network speeds and macOS count in 1,000s: 1 GB = 1,000,000,000 bytes. Switch to 1,024 to read KB, MB and GB the way Windows and RAM sizes use them.
Type a size in plain words — “1 TB to GiB”, “500 GB in MB”, “8 Mb to MB”, “4096 bytes to KiB” — or use the boxes below.
Exact · MB = GB × 1,000
- Gigabyte: 1,000,000,000 bytes (10⁹)
- Megabyte: 1,000,000 bytes (10⁶)
Why does my 1 TB drive show 931 GB?
Drive makers count in powers of 1,000, so a 1 TB drive holds 1,000,000,000,000 bytes. Windows divides by 1,024 instead but still writes “GB”, so the same bytes look like fewer gigabytes. Type the capacity printed on the box:
1,000,000,000,000 bytes ÷ 1,024³ (1,073,741,824) ≈ 931.32 GiB. Windows writes that as “931 GB” instead of 1,000 GB: a 6.87 % smaller number for the same bytes, because each binary unit is bigger. Nothing is missing — formatting and system files then take a little more space.
Common capacities and what Windows shows
| On the box | Bytes | Windows shows about | Exact binary size |
|---|---|---|---|
| 128 GB | 128,000,000,000 | 119 GB | 119.21 GiB |
| 256 GB | 256,000,000,000 | 238 GB | 238.42 GiB |
| 500 GB | 500,000,000,000 | 465 GB | 465.66 GiB |
| 512 GB | 512,000,000,000 | 476 GB | 476.84 GiB |
| 1 TB | 1,000,000,000,000 | 931 GB | 931.32 GiB |
| 2 TB | 2,000,000,000,000 | 1.81 TB | 1.82 TiB |
| 4 TB | 4,000,000,000,000 | 3.63 TB | 3.64 TiB |
| 8 TB | 8,000,000,000,000 | 7.27 TB | 7.28 TiB |
| 16 TB | 16,000,000,000,000 | 14.5 TB | 14.55 TiB |
| 24 TB | 24,000,000,000,000 | 21.8 TB | 21.83 TiB |
Windows figures are cut to three significant digits; the space you can use is a little less again after formatting.
1 GB in every unit
Select a unit to convert to it. Values marked ≈ are rounded; all others are exact.
| Unit | Value | Copy |
|---|---|---|
| Bytes, decimal (SI: ×1000) | ||
| 1,00,00,00,000 | ||
| 10,00,000 | ||
| to | 1,000 | |
| from | 1 | |
| 0.001 | ||
| 0.000001 | ||
| 1 × 10⁻⁹ | ||
| 1 × 10⁻¹² | ||
| 1 × 10⁻¹⁵ | ||
| 1 × 10⁻¹⁸ | ||
| 1 × 10⁻²¹ | ||
| Bytes, binary (IEC: ×1024) | ||
| 9,76,562.5 | ||
| 953.67431640625 | ||
| ≈ 0.9313225746 | ||
| ≈ 0.0009094947018 | ||
| ≈ 8.881784197 × 10⁻⁷ | ||
| ≈ 8.67361738 × 10⁻¹⁰ | ||
| ≈ 8.470329473 × 10⁻¹³ | ||
| ≈ 8.271806126 × 10⁻¹⁶ | ||
| ≈ 8.077935669 × 10⁻¹⁹ | ||
| ≈ 7.888609052 × 10⁻²² | ||
| Bits, decimal | ||
| 8,00,00,00,000 | ||
| 2,00,00,00,000 | ||
| 80,00,000 | ||
| 8,000 | ||
| 8 | ||
| 0.008 | ||
| 0.000008 | ||
| Bits, binary | ||
| 78,12,500 | ||
| 7,629.39453125 | ||
| 7.450580596923828125 | ||
| ≈ 0.007275957614 | ||
Convert a list of values
Up to 1,000 lines. Fractions (3/4), mixed numbers (1 1/2) and grouped digits (1,250) are fine.
| Value | Result |
|---|
Decimal and binary prefixes side by side
SI prefixes are powers of 10; the IEC binary prefixes (with an i) are powers of 2. The gap grows with every step.
| Decimal (SI) | Bytes | Binary (IEC) | Bytes | Binary is bigger by |
|---|---|---|---|---|
| kilo (kB) | 1,000 | kibi (KiB) | 1,024 | 2.4 % |
| mega (MB) | 1,000,000 | mebi (MiB) | 1,048,576 | 4.86 % |
| giga (GB) | 1,000,000,000 | gibi (GiB) | 1,073,741,824 | 7.37 % |
| tera (TB) | 10¹² | tebi (TiB) | 2⁴⁰ | 9.95 % |
| peta (PB) | 10¹⁵ | pebi (PiB) | 2⁵⁰ | 12.59 % |
| exa (EB) | 10¹⁸ | exbi (EiB) | 2⁶⁰ | 15.29 % |
| zetta (ZB) | 10²¹ | zebi (ZiB) | 2⁷⁰ | 18.06 % |
| yotta (YB) | 10²⁴ | yobi (YiB) | 2⁸⁰ | 20.89 % |
| ronna (RB) | 10²⁷ | robi (RiB) | 2⁹⁰ | 23.79 % |
| quetta (QB) | 10³⁰ | quebi (QiB) | 2¹⁰⁰ | 26.77 % |
About the Data Storage Converter
Convert data sizes between bits, bytes and every prefix: decimal SI units (kB, MB, GB, TB, PB and up to QB) and binary IEC units (KiB, MiB, GiB, TiB, PiB and up to QiB). Type in either box and the other updates; the table underneath shows the size in every unit at once, and the byte count is always exact — 1 TiB is 1,099,511,627,776 bytes, not an approximation.
The two families are the reason a 1 TB drive appears as 931 GB. Drive makers count in powers of 1,000, while Windows counts in powers of 1,024 and still writes “GB”. The explainer under the result turns the capacity on the box into the figure Windows shows and the exact binary size, and a switch at the top decides whether “KB”, “MB” and “GB” without an i mean 1,000 or 1,024.
How to use it
- Type a number in From and pick its unit, then pick the unit you want in To — or type
1 TB to GiBin Quick convert and press Enter. - Choose what plain “KB”, “MB” and “GB” mean at the top: powers of 1,000 (SI, as on drives and network plans) or powers of 1,024 (as Windows and memory sizes use them). Units with an i, such as MiB, always mean 1,024.
- Under Why does my 1 TB drive show 931 GB? type the capacity printed on a drive or memory card to see the bytes, the figure Windows shows and the exact binary size.
- Copy the result or a link, download the table of every unit as CSV, or open Convert a list for a column of sizes.
Examples
1 TB to GiB
931.3225746 GiB
10¹² bytes ÷ 1,024³ = 931.32. Windows shows it as “931 GB”.
1 GB to MB
1,000 MB
In binary units 1 GiB = 1,024 MiB. Switch the KB setting to 1,024 to read GB and MB that way.
8 GiB to B
8,589,934,592 bytes
Memory is traditionally sized in powers of two, so an “8 GB” module holds 8 GiB.
25 MB to MiB
23.84185791 MiB
1 Gbit to MB
125 MB
8 bits make a byte, so divide bits by 8: 1,000,000,000 ÷ 8 = 125,000,000 bytes.
4 KiB to B
4,096 bytes
Common uses
- Working out why a new drive, memory card or phone shows less space than the box says.
- Comparing file sizes reported by different systems: Windows (binary), macOS and drive labels (decimal), Linux tools (either).
- Converting between bits and bytes for network transfers, chip densities and file sizes.
- Sizing storage, backups and cloud quotas in TB, TiB and PB.
- Programming and documentation: exact byte counts for KiB, MiB and GiB buffers.
Decimal (SI) and binary (IEC) units
SI prefixes are powers of 10: 1 kB = 1,000 bytes, 1 MB = 1,000,000 bytes, 1 GB = 10⁹ bytes. The BIPM SI Brochure (9th edition, version 4.01) says they “should not be used to indicate powers of 2 (for example, one kilobit represents 1000 bits and not 1024 bits)” and lists the binary prefixes of IEC 80000-13 for that job: kibi (Ki) = 2¹⁰ = 1,024, mebi (Mi) = 2²⁰ = 1,048,576, gibi (Gi) = 2³⁰, tebi (Ti), pebi (Pi), exbi (Ei), zebi (Zi), yobi (Yi), robi (Ri) and quebi (Qi) = 2¹⁰⁰. NIST explains the same prefixes on its binary multiples page.
The two families drift apart with every step: a KiB is 2.4 % bigger than a kB, a GiB 7.37 % bigger than a GB and a TiB 9.95 % bigger than a TB. The table at the bottom of the page lists every prefix.
Why your drive shows less space than the box
Seagate’s support article on reported capacity explains that drives are marketed in decimal units while “Windows, and older versions of macOS use the binary (base 2) numbering system”: a 1 TB drive appears as 931 GB, a 2 TB drive as 1.81 TB and a 4 TB drive as 3.63 TB. The bytes are all there; Windows divides by 1,024³ and labels the result GB.
Apple’s storage capacity article says OS X Leopard and earlier and iOS 10 and earlier reported binary units, and that a device’s “actual formatted capacity” is less than the label because formatting and the operating system use space. On Linux, df -h and ls -lh use powers of 1,024 and df --si uses powers of 1,000 (GNU coreutils manual).
What “KB” means where
- kB (small k) is the SI symbol: 1,000 bytes.
- KB (capital K) is not an SI symbol. Windows uses it for 1,024 bytes, and so do memory sizes; many other programs use it for 1,000 bytes.
- KiB always means 1,024 bytes, and MiB, GiB and TiB likewise always mean powers of 1,024.
- A small b is a bit and a capital B a byte: 8 Mb (megabits) is 1 MB.
The switch at the top of the converter sets how Quick convert reads plain KB, MB and GB; the unit lists always show both families separately, so a conversion never depends on guessing.
Limitations
- The space you can actually use is less than the raw capacity because of formatting, file-system overhead and recovery or system partitions; how much depends on the device and is not calculated here.
- The Windows figure imitates File Explorer: three significant digits, cut rather than rounded (2 TB shows as 1.81 TB although it is 1.819 TiB), and from 1,000 of a unit the next unit up (1,000 GiB shows as 0.97 TB). Other programs may round differently.
- Sizes that do not fit in about 24 digits are shown in scientific notation; the underlying arithmetic stays exact.
- Words such as “block”, “sector” or “word” have no fixed size and are not converted.
Privacy
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Frequently asked questions
How many MB are in a GB?
1,000 in decimal units (1 GB = 1,000 MB = 1,000,000,000 bytes). In binary units 1 GiB = 1,024 MiB = 1,073,741,824 bytes. Windows labels the binary units GB and MB, which is why both answers are common.
Why does my 1 TB drive show 931 GB?
The drive has 1,000,000,000,000 bytes. Windows divides by 1,024³ = 1,073,741,824 and gets 931.32, which it writes as “931 GB”. Nothing is missing; the unit is different. Formatting then takes a little more.
Is a kilobyte 1,000 or 1,024 bytes?
In the SI, a kilobyte (kB) is exactly 1,000 bytes; 1,024 bytes is a kibibyte (KiB). Some software still calls 1,024 bytes a “KB”, so check which one a figure uses — the switch at the top of this page lets you read plain KB either way.
How many bits are in a byte?
Eight. A byte is also called an octet, so 1 kB = 8,000 bits and 1 KiB = 8,192 bits.
Is Mb the same as MB?
No. Mb (or Mbit) is a megabit and MB a megabyte, eight times larger. Internet plans are sold in megabits per second — see the Data Rate Converter to turn Mbps into MB/s.
What is a GiB?
A gibibyte: 2³⁰ = 1,073,741,824 bytes, about 7.37 % more than a gigabyte (10⁹ bytes). The “i” marks the binary prefixes standardised in IEC 80000-13.