How to use
- Enter a value and pick the units to convert from and to. The table lists the same size in every unit.
- The arrow button swaps the two units.
- In Download time, enter a file size and your connection speed in Mbps to see the theoretical transfer time.
Decimal (SI) vs binary (IEC) units
“Kilo” has two meanings in computing. In the SI system it means 1000; in 1998 the IEC introduced separate binary prefixes — kibi (Ki), mebi (Mi), gibi (Gi) — for powers of 1024.
| SI unit | Bytes | IEC unit | Bytes |
|---|---|---|---|
| 1 KB | 1,000 | 1 KiB | 1,024 |
| 1 MB | 1,000,000 | 1 MiB | 1,048,576 |
| 1 GB | 10⁹ | 1 GiB | 1,073,741,824 |
| 1 TB | 10¹² | 1 TiB | 1,099,511,627,776 |
One byte (B) is 8 bits.
Why a 500 GB drive shows about 465 GB in Windows
Drive makers label capacity in SI units, where 1 GB = 10⁹ bytes. Windows calculates in powers of 1024 but still calls the result “GB”. A 500 GB drive holds 500 × 10⁹ bytes, and 500 × 10⁹ ÷ 1024³ ≈ 465.66 GiB — nothing is missing, the units are just different. For the same reason a 1 TB drive shows up as about 931 GB. macOS has reported sizes in base 1000 since Snow Leopard (2009).
Download time
Connection speeds are quoted in megabits per second (Mbps), while file sizes are in megabytes. Since 1 byte = 8 bits, 100 Mbps moves at most 12.5 MB per second.
- A 4 GB file at 100 Mbps takes 4 × 8,000 ÷ 100 = 320 seconds (5 min 20 s).
- The same file at 1 Gbps (1,000 Mbps) takes 32 seconds.
These are best-case figures. Real downloads take longer because of TCP/IP overhead, Wi-Fi conditions and server speed.
FAQ
How many GB are in a TB?
Exactly 1,000 GB in SI units, or about 931.32 GiB in binary units.
Is a kilobyte 1000 or 1024 bytes?
By the SI and IEC standards, 1 KB = 1000 bytes and 1 KiB = 1024 bytes. Many places — Windows Explorer and RAM sizes, for example — still use “KB” to mean 1024 bytes by convention.
Can I check the size of text or Base64 data?
Use the character counter for the byte size of text, and the Base64 encoder/decoder to see encoded output, which is about 33% larger than the original.