Online Tool Store
Data Size Converter
Convert between bits, bytes and every decimal and binary prefix at once, see why a 1 TB drive reads as 931 GB, and estimate transfer time.
🔒 This tool runs entirely in your browser. Your files are never uploaded to a server.
In bytes
—
Decimal — powers of 1000
What drive makers, network operators and SI use
Binary — powers of 1024
What operating systems and RAM sizes actually count in
How long would it take to transfer?
How to use it
- Enter the amount and pick its unit — the list is grouped by convention.
- Read the two tables: decimal on the left, binary on the right.
- The amber note shows the same bytes on both rulers, which is the answer to most drive-size questions.
- Add a connection speed to see how long moving it would take.
Two rulers, one pile of bytes
Every conversion here goes through a byte count, and then divides by one of two things: a power of 1000, or a power of 1024. That single choice is what produces the "missing" storage everyone notices:
1 TB = 1,000,000,000,000 bytes
÷ 1000³ = 1,000.00 GB ← how it was sold
÷ 1024³ = 931.32 GiB ← what Windows shows, labelled GB
The two rulers drift apart as the prefixes stack up, because each level multiplies the 2.4% difference again:
kB → KiB +2.40%
MB → MiB +4.86%
GB → GiB +7.37%
TB → TiB +9.95%
PB → PiB +12.59%
So a 500 GB drive reads as 465.66 GiB and a 2 TB drive as 1.819 TiB. Neither number is wrong; they are answers to different questions. The IEC added the kibi/mebi/gibi prefixes in 1998 to make the distinction sayable, and the remaining confusion is entirely down to software that reports binary values with decimal labels.
Bits, bytes, and the case of one letter
Connection speeds are quoted in bits per second and files are measured in bytes, and the only thing separating the two notations is the case of the b:
100 Mbps ÷ 8 = 12.5 MB/s
1 Gbps ÷ 8 = 125 MB/s
25 GB at 100 Mbps → 2,000 s ≈ 33 minutes
That factor of eight is why a connection advertised as "100 Meg" never fills a progress bar as fast as the number suggests. The transfer estimate here is the clean arithmetic; real transfers lose a few per cent to protocol overhead and rather more if the disk, not the link, is the slow part.
Where the exactness stops
Byte counts are integers, and a JavaScript number is a double, so it can represent every integer only up to 9,007,199,254,740,991 — which is 8 PiB. Above that the tool says the figures are approximate instead of printing spurious digits. There is a pleasing coincidence at the boundary: one pebibyte expressed in bits is 2⁵⁰ × 8, which is exactly 2⁵³, the last integer a double counts reliably.
FAQ
Why does my 1 TB drive show as 931 GB?
Nothing is missing. The drive holds 1,000,000,000,000 bytes, which is exactly 1 TB by the decimal definition the manufacturer used. Your operating system divides by 1024 three times instead and calls the result GB, giving 931.32. Same bytes, different ruler — and the gap grows with size: 2.4% at kilobytes, 7.37% at gigabytes, 9.95% at terabytes.
What is the difference between KB and KiB?
A kilobyte is 1,000 bytes; a kibibyte is 1,024. The IEC introduced the -bi- prefixes in 1998 precisely to end the ambiguity, so KiB, MiB and GiB always mean powers of 1024 and kB, MB and GB should always mean powers of 1000. Software adoption has been patchy: macOS and Linux now report decimal GB, Windows still reports binary values labelled GB.
Why is my 100 Mbps connection only downloading at 12 MB/s?
Because those are bits and bytes. There are eight bits in a byte, so 100 megabits per second is 12.5 megabytes per second — and that is the theoretical ceiling before protocol overhead takes a few per cent. Network speeds are quoted in bits, file sizes in bytes, and the lower-case b against the upper-case B is the only thing distinguishing them.
Which unit should I use in my own writing?
Pick one convention and label it. If you mean 1024 bytes, write KiB. If you mean 1000, write kB. The one thing to avoid is "GB" for a binary quantity, which is what causes the confusion in the first place.
How accurate is the transfer time?
It is the arithmetic answer — size divided by speed — and it deliberately ignores overhead. Real transfers lose a few per cent to TCP and framing, more on a congested or high-latency link, and a lot more if the bottleneck turns out to be the disk rather than the network.
Is it exact for very large numbers?
Up to 8 PiB it is exact to the byte. Past that a double cannot hold every integer, and the tool says so rather than presenting a rounded figure as precise. Curiously, one pebibyte in bits is exactly 2⁵³ — the last integer a double can count to reliably.
How we compare
| Feature | Online Tool Store | Search-box conversion | Most unit converters |
|---|---|---|---|
| Keeps decimal and binary strictly separate | ✓ | Often conflated | Frequently conflated |
| Shows both rulers at once | ✓ | ✗ | ✗ |
| Explains the drive-label gap with the numbers | ✓ | ✗ | ✗ |
| Bits, bytes and transfer time together | ✓ | ✗ | Rarely |
| States where precision runs out | ✓ | ✗ | ✗ |
| Answers without leaving the page you are on | ✗ | ✓ | ✗ |
| Dozens of other unit families | ✗ | ✓ | ✓ |
A search box will convert a number faster than this page will load. What it will not do is show you both conventions side by side, name the 7.37% gap that made your drive look small, or tell you where the arithmetic stops being exact — which is the reason to come here rather than there.