Data Storage Unit Converter (TB, GB, MB, PB — Binary vs Decimal)
Two incompatible conventions have coexisted for decades. Storage manufacturers use decimal SI prefixes where a gigabyte is 1,000,000,000 bytes; operating systems traditionally use binary powers where the same word means 1,073,741,824 bytes. The seven percent gap at gigabyte scale widens to nine percent at terabyte scale.
Drive manufacturers use decimal; Windows reports binary — which is exactly why capacities appear to shrink after purchase.
| Unit | Decimal (1000) | Binary (1024) | IEC name |
|---|---|---|---|
| B | 1,000,000,000,000.00 | 1,000,000,000,000.00 | B |
| KB | 1,000,000,000.00 | 976,562,500.00 | KiB |
| MB | 1,000,000.00 | 953,674.32 | MiB |
| GB | 1,000.0000 | 931.3226 | GiB |
| TB | 1.0000 | 0.9095 | TiB |
| PB | 0.0010 | 0.0009 | PiB |
Why a 1 TB drive shows 931 GB
The manufacturer sells one trillion bytes. Windows divides by 1024 three times, yielding 931.32 GiB, and labels the result 'GB'. Nothing is missing and nothing is faulty — the same bytes are simply being counted with a different divisor. macOS switched to decimal reporting in 2009 and shows the full 1 TB.
The IEC prefixes nobody adopted
In 1998 the IEC standardised kibibyte, mebibyte and gibibyte for the binary values, reserving kilobyte and megabyte for decimal. Linux tooling and RAM specifications largely follow it; Windows, most consumer software and everyday speech do not. When precision matters, state the byte count explicitly.
Where each convention is used
RAM is always binary, because memory addressing is inherently a power of two. Hard drives, SSDs and network speeds are decimal. File sizes reported by operating systems vary by platform. Cloud storage billing is almost universally decimal, which quietly favours the provider by a few percent.
Decimal versus binary at every scale
| Unit | Decimal bytes | Binary bytes | Difference | Advertised 1 unit shows as |
|---|---|---|---|---|
| KB / KiB | 1,000 | 1,024 | 2.4% | 0.977 KiB |
| MB / MiB | 1,000,000 | 1,048,576 | 4.9% | 0.954 MiB |
| GB / GiB | 1,000,000,000 | 1,073,741,824 | 7.4% | 0.931 GiB |
| TB / TiB | 10^12 | 1,099,511,627,776 | 10.0% | 0.909 TiB |
| PB / PiB | 10^15 | 2^50 | 12.6% | 0.888 PiB |
People also ask
Why does my 1TB drive only show 931GB?
The manufacturer counts one trillion bytes in decimal; Windows divides by 1024 three times and reports 931 GiB while labelling it GB. No capacity is lost.
What is the difference between a gigabyte and a gibibyte?
A gigabyte is 1,000,000,000 bytes; a gibibyte is 1,073,741,824 bytes — about 7.4% larger.
Which base do cloud providers use for billing?
Almost all major providers bill in decimal gigabytes, so a 100 GB allowance is 100,000,000,000 bytes, not 107 billion.
Three worked examples
Same engine, three different starting points — useful if you want to see how sensitive the answer is before you type your own numbers in.
Example 1: value 0.78, from unit "GB"
On the lower / more conservative end. Drive manufacturers use decimal; Windows reports binary — which is exactly why capacities appear to shrink after purchase.
Example 2: value 1, from unit "TB"
A typical middle-of-the-road setup. Drive manufacturers use decimal; Windows reports binary — which is exactly why capacities appear to shrink after purchase.
Example 3: value 1.3, from unit "PB"
On the higher / more demanding end. Drive manufacturers use decimal; Windows reports binary — which is exactly why capacities appear to shrink after purchase.
Quick answers about the Data Storage Unit Converter
What exactly does the Data Storage Unit Converter work out?
Two incompatible conventions have coexisted for decades. You enter value, from unit and base and the result panel updates straight away, so you can compare two or three versions of the same question in a few seconds.
What do I need before I start?
Only 3 fields: value, from unit and base. Nothing else is needed and nothing is stored.
How is it calculated — why a 1 TB drive shows 931 GB?
The manufacturer sells one trillion bytes. The same maths runs inside this page, so hand-checking the result on paper gives you the identical figure.
Why do two calculators give me different answers for data Storage Unit?
In 1998 the IEC standardised kibibyte, mebibyte and gibibyte for the binary values, reserving kilobyte and megabyte for decimal. Different sites pick different assumptions, so always check which method a calculator states before you trust the gap between two numbers.
What does the "Decimal versus binary at every scale" table on this page tell me?
It is the reference range this tool works against — 5 rows from "KB / KiB" (1,000) up to "PB / PiB" (10^15). Use it to sanity-check whether the number you just calculated sits where you expected it to.
Which from unit should I pick?
The dropdown offers 6 choices — B, KB, MB, GB, TB and PB. Pick the one that matches your real situation rather than the one you would like to be true; from unit usually moves the final figure more than any other single input, so it is worth running it twice with the option above and below your guess.
Does it work in both metric and imperial (or another currency)?
Yes. The "From unit" control converts every field and every result, so you never have to convert anything by hand before typing it in. Switch it after entering your numbers and the output re-renders instantly in the new system.
Do I have to press a button or reload the page to see the result?
No. Data Storage Unit Converter runs completely inside your browser, so the moment you change a value the cards recalculate — there is no submit step, no page reload and no waiting for a server round trip. That also means it keeps working on a weak or intermittent mobile connection.
Is it free, and do you keep what I type?
It is free with no sign-up, no app install and no usage limit. Nothing you enter into Data Storage Unit Converter leaves your device — the calculation is JavaScript running locally, so there is no upload of your figures to DrHint or anyone else.
Can I use it on a phone?
Yes — the layout stacks to a single column on small screens and the number fields open the numeric keypad on both Android and iOS. Many people bookmark this page or add it to their home screen and re-open it whenever the question comes up.
Anything to be careful about with the result?
The manufacturer counts one trillion bytes in decimal; Windows divides by 1024 three times and reports 931 GiB while labelling it GB. Treat the output as a well-grounded estimate for planning, not as a professional, legal or medical decision on its own.
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