There are two families of storage units. SI (decimal) prefixes count in powers of 1,000: 1 kB = 1,000 bytes, 1 GB = 10⁹ bytes, 1 TB = 10¹² bytes. The IEC binary prefixes count in powers of 1,024: 1 KiB = 1,024 bytes, 1 GiB = 2³⁰ bytes, 1 TiB = 2⁴⁰ bytes. NIST's page on these prefixes (approved by the IEC in 1998) spells out the difference: 1 MB = 1,000,000 bytes, while 1 MiB = 1,048,576 bytes.
Drive makers label capacity in decimal units, while some operating systems report binary units but still print "GB". That is why a 1 TB drive shows about 931 GB (really 931.32 GiB); no space is missing.
How to use the data storage converter
- Enter the amount.
- Choose the unit you have and the one you want. Units ending in "iB" are binary (1,024-based).
- Read the result and the table of every unit. 1 byte = 8 bits.
Formula
Worked example
How much does a "1 TB" drive show in binary units?
- 1 TB = 1,000,000,000,000 bytes.
- 1 GiB = 1,073,741,824 bytes.
- 10¹² ÷ 1,073,741,824 = 931.32 GiB (or 0.9095 TiB).
Similarly, a 500 GB drive is 465.66 GiB, and a 4 GiB memory module is 4.295 GB.
Decimal vs binary gap
| Decimal unit | Binary unit | Binary is larger by |
|---|---|---|
| kB (10³) | KiB (2¹⁰) | 2.4% |
| MB (10⁶) | MiB (2²⁰) | 4.9% |
| GB (10⁹) | GiB (2³⁰) | 7.4% |
| TB (10¹²) | TiB (2⁴⁰) | 10.0% |
Network speeds are usually given in bits per second (Mbps), so divide by 8 to get bytes: 100 Mbps is 12.5 MB/s at best, before overhead. Formatted capacity is also slightly lower than the raw figure because the file system uses some space.
Bits vs bytes for internet speeds
Internet plans and Wi-Fi speeds are quoted in megabits per second (Mbps), while file sizes and download managers usually show megabytes (MB). Since 1 byte = 8 bits, divide Mbps by 8 for the best-case MB per second:
| Plan speed | Best case MB/s | Time for a 5 GB file (ideal) |
|---|---|---|
| 50 Mbps | 6.25 | 13 min 20 s |
| 100 Mbps | 12.5 | 6 min 40 s |
| 500 Mbps | 62.5 | 1 min 20 s |
| 1,000 Mbps (1 Gbps) | 125 | 40 s |
Real downloads are slower because of protocol overhead, Wi-Fi conditions and the server's own speed.
Estimating how much fits
To estimate how many files fit on a drive, divide the usable capacity by the typical file size, using the same unit family for both. For example, a 256 GB phone holds roughly 256,000 MB; at an average of 4 MB per photo that is about 64,000 photos before accounting for the operating system and apps, which take a meaningful share. Use the decimal units here if the file sizes are shown by a system that counts in 1,000s, and the binary units (MiB, GiB) if it counts in 1,024s.
Caveats and assumptions
- Some software uses "KB/MB/GB" to mean 1,024-based units; check which convention your tool uses.
- Network throughput in bits per second also loses some capacity to protocol overhead.
Frequently asked questions
Why does my 1 TB drive show 931 GB?
The drive has 10¹² bytes. Your computer divides by 1,024³ instead of 1,000³, giving 931.32 "GB" (properly GiB).
How many MB are in a GB?
1,000 MB in decimal units. In binary units, 1 GiB = 1,024 MiB.
What is the difference between GB and GiB?
A GB is 1,000,000,000 bytes; a GiB is 1,073,741,824 bytes, about 7.4% more.
How many bits are in a byte?
8 bits.
How many GB is a TB?
1,000 GB in decimal units; 1 TiB = 1,024 GiB in binary units.
How fast is 100 Mbps in MB/s?
At most 12.5 MB/s (100 ÷ 8), before overhead.
Sources
- NIST — Prefixes for binary multiples — IEC kibi, mebi, gibi, tebi; examples comparing MB/MiB and GB/GiB
This calculator gives estimates for planning and education. Check measurements, local codes, supplier specs and your school's official policy before relying on a result. See our disclaimer and how we build and check calculators.