Data Size Converter
Type a number once — see it in every data unit, decimal and binary, instantly.
Enter a number to see it in every unit.
All units at once
| Bit (b) | — |
| Byte (B) | — |
Decimal (SI, 1000) vs Binary (IEC, 1024)
| Decimal (SI · ×1000) | Binary (IEC · ×1024) |
|---|---|
| kB— | KiB— |
| MB— | MiB— |
| GB— | GiB— |
| TB— | TiB— |
| PB— | PiB— |
Why the same number of bytes shows two different sizes
Every digital measurement starts from the bit — a single 0 or 1. Group eight bits and you get a byte, the unit computers use to address memory and files. The trouble starts one step up: once you scale a byte count into kilo-, mega-, giga- or larger units, there are two competing counting systems in everyday use, and they assign the same prefix to two different sizes. Drive makers, network providers and most marketing use the decimal (SI) system, where each step is ×1000. Operating systems reporting free space, and RAM specifications, use the binary (IEC) system, where each step is ×1024. A number without knowing which system produced it is not really a number yet — that ambiguity is the exact problem this converter is built to remove, by showing both readings for the same input at once.
How to read the converter
- Type the quantity into the Value field — any positive or fractional number.
- Pick the unit you already have in From: the single Bit option, one of the six decimal SI units (B, kB, MB, GB, TB, PB), or one of the five binary IEC units (KiB, MiB, GiB, TiB, PiB).
- Pick the unit you want in To, or skip it entirely and scan the "All units at once" table, which fills in every unit for the same input in one pass.
- Use the ⇄ button to flip From and To without retyping the value.
- The decimal-vs-binary comparison table lines kB against KiB, MB against MiB, GB against GiB and so on, so the gap between the two systems for your specific number is visible directly, not just as a rule of thumb.
The math behind the two systems
Decimal (SI) steps by powers of 1000: 1 kB = 1000¹ B = 1,000 B · 1 MB = 1000² B = 1,000,000 B · 1 GB = 1000³ B = 1,000,000,000 B.
Binary (IEC) steps by powers of 1024: 1 KiB = 1024¹ B = 1,024 B · 1 MiB = 1024² B = 1,048,576 B · 1 GiB = 1024³ B = 1,073,741,824 B.
At any given step n (kilo = 1, mega = 2, giga = 3 …), the binary unit is larger than the decimal unit by a factor of (1024/1000)n. At the giga step that factor is 1.0737, which is why 1 GB (decimal) equals 1 / 1.0737 ≈ 0.9313 GiB (binary) — the two numbers describe the identical byte count, just measured in different-sized buckets.
Worked examples
1. A "4.7 GB" DVD image. The disc is labeled in decimal by the manufacturer: 4.7 GB = 4.7 × 1,000,000,000 B = 4,700,000,000 bytes. Your file manager reports size in binary, dividing by 1,073,741,824 (1024³): 4,700,000,000 ÷ 1,073,741,824 ≈ 4.377 GiB, usually rounded and labeled "4.38 GB" or "4.4 GB" — the file did not shrink, it is the same bytes read through the binary ruler.
2. Downloading over a 200 Mbps connection. Internet speed is quoted in megabits per second; file size is in megabytes. Convert by dividing by 8: 200 Mbps ÷ 8 = 25 MB/s. A 2,000 MB update at that speed takes 2,000 ÷ 25 = 80 seconds under ideal conditions, before protocol overhead and real-world throughput losses.
3. "16 GB" of RAM showing as less in Task Manager. Memory modules are sized in binary: 16 GB of RAM is really 16 GiB = 16 × 1,073,741,824 = 17,179,869,184 bytes. Some tools display that same byte count using a decimal GB label (17.18 GB), and part of the address space is also reserved for firmware/system use — two separate reasons the number you see rarely matches "16" exactly.
Reference table: decimal vs binary at every step
| Step | Decimal unit | Decimal bytes | Binary unit | Binary bytes | Binary ÷ decimal |
|---|---|---|---|---|---|
| kilo / kibi | kB | 1,000 | KiB | 1,024 | 1.024 |
| mega / mebi | MB | 1,000,000 | MiB | 1,048,576 | 1.049 |
| giga / gibi | GB | 1,000,000,000 | GiB | 1,073,741,824 | 1.074 |
| tera / tebi | TB | 1,000,000,000,000 | TiB | 1,099,511,627,776 | 1.100 |
| peta / pebi | PB | 1,000,000,000,000,000 | PiB | 1,125,899,906,842,624 | 1.126 |
Common mistakes and label traps
- Treating a spec-sheet "GB" and an OS-reported "GB" as the same number. One is usually decimal (packaging, storage marketing); the other is often binary math wearing a decimal label (classic Windows Explorer behavior, some older macOS builds).
- Skipping the ÷8 step between bits and bytes. Confusing megabits (Mb, network speed) with megabytes (MB, file size) is the single most common error in download-time estimates.
- Assuming the decimal/binary gap is constant. It grows with the exponent: about 2.4% at kilo, 4.9% at mega, 7.4% at giga, 10% at tera. That is why a "2 TB" drive appears to lose roughly 90 GB to the binary/decimal mismatch, while a "2 GB" file only loses about 49 MB — same root cause, very different visible impact.
- Reading lower-case "b" and upper-case "B" as interchangeable. They are not — b is bit, B is byte, an 8× difference. Use the dedicated Bit option in this converter rather than eyeballing the case.
What this tool does not cover
This converter performs exact unit math for storage and data-transfer sizes. It does not model filesystem overhead (block size, metadata, journaling), compression ratios, or the capacity vendors reserve separately for SSD wear-leveling and drive formatting. The "free space" a real device reports will always run a little below the raw byte arithmetic shown here, because the filesystem itself consumes part of the underlying capacity.
Sources & further reading
Frequently asked questions
MB to GB — is it 1000 or 1024?
Both are used, which is exactly the confusion this converter clears up. In the decimal SI system (used by drive makers, networks and most marketing), 1 GB = 1000 MB and 1 MB = 1000 kB. In the binary IEC system (used by Windows and RAM), the correct names are KiB, MiB and GiB, where 1 GiB = 1024 MiB. So 1 GB (decimal) = 0.9313 GiB (binary). This tool shows both columns side by side so you never have to guess which one a number means.
Why does my 1 TB drive show as only ~931 GB?
Because the drive maker counts in decimal (1 TB = 1,000,000,000,000 bytes) while your operating system divides by 1024 and still labels the result "GB". 1 TB = 1000 GB in decimal, but only 0.9095 TB when measured in binary tebibytes — that is 931.32 GiB, which Windows displays as "931 GB". No space is missing; the two systems just count differently. Type 1 and pick TB to see the TiB / GiB figure instantly.
Megabit (Mb) vs megabyte (MB) — what is the difference?
One byte is 8 bits, so a megabyte is 8× a megabit. Internet speeds are quoted in megabits per second (Mbps), while file sizes and download managers use megabytes (MB). That is why a 100 Mbps connection tops out around 12.5 MB/s. Enter a value with the bit unit selected to convert between the two and avoid the 8× trap.
How precise are the results?
Every conversion keeps up to 10 significant figures, then trailing zeros are trimmed for readability. Very large or very small numbers (roughly 1e15 and above, or below 1e-9) switch to scientific notation, so nothing is silently rounded away to zero. All values come from the exact byte definition of each unit — decimal units are powers of 1000, binary units are powers of 1024.
Is my input sent to a server?
No. This data size converter runs entirely in your browser — the number you type is never uploaded anywhere. The only thing saved is your last chosen unit pair (for example MB → GB), kept in your browser's local storage so it is ready next time. The value itself is not stored.