Data storage units confuse almost everyone. Your phone has 128 “gigabytes” but your internet speed is measured in “megabits.” Your 1 TB hard drive shows only 931 GB when you plug it in. And somewhere along the way, the industry created two different definitions of “gigabyte” that differ by 7%. This guide cuts through the confusion with clear explanations and practical context for every unit.
| Unit | Abbreviation | Size (Decimal) | Real-World Scale |
|---|---|---|---|
| Bit | b | 1 or 0 | Single binary digit |
| Byte | B | 8 bits | One character of text |
| Kilobyte | KB | 1,000 bytes | Short email (2–5 KB) |
| Megabyte | MB | 1,000 KB | 1 MP3 song (3–5 MB) |
| Gigabyte | GB | 1,000 MB | 1 hour of SD video |
| Terabyte | TB | 1,000 GB | ~250,000 photos |
| Petabyte | PB | 1,000 TB | Netflix’s content library |
| Exabyte | EB | 1,000 PB | All words ever spoken (~5 EB) |
This is the single most confusing aspect of data storage. The computing industry uses two different counting systems:
Decimal (SI): Used by storage manufacturers. 1 KB = 1,000 bytes, 1 MB = 1,000,000 bytes, 1 GB = 1,000,000,000 bytes. This is how your hard drive, SSD, or USB drive is labeled.
Binary (IEC): Used by operating systems. 1 KiB = 1,024 bytes, 1 MiB = 1,048,576 bytes, 1 GiB = 1,073,741,824 bytes. This is how Windows, macOS, and Linux report storage capacity.
| Advertised (Decimal) | OS Shows (Binary) | “Missing” |
|---|---|---|
| 128 GB | 119.2 GiB | ~7% |
| 256 GB | 238.4 GiB | ~7% |
| 512 GB | 476.8 GiB | ~7% |
| 1 TB | 931.3 GiB | ~7% |
| 2 TB | 1,862.6 GiB | ~7% |
No storage is actually missing. The drive contains exactly the number of bytes advertised. The discrepancy is purely a labeling difference between decimal and binary counting.
The math: 1 TB = 1,000,000,000,000 bytes. Divide by 1,024 three times to convert to GiB: 1,000,000,000,000 ÷ 1,024³ = 931.3 GiB. Use the Data Storage Converter for instant conversions between all units.
Internet speeds are measured in bits per second (Mbps), while file sizes are measured in bytes (MB). Since there are 8 bits in a byte, divide your internet speed by 8 to find your download rate in megabytes per second. A 100 Mbps connection downloads at approximately 12.5 MB/s. A 1 Gbps connection downloads at about 125 MB/s.
| Connection Speed | Download Rate | Time for 1 GB File |
|---|---|---|
| 25 Mbps | ~3.1 MB/s | ~5 min 20 sec |
| 100 Mbps | ~12.5 MB/s | ~1 min 20 sec |
| 300 Mbps | ~37.5 MB/s | ~27 sec |
| 1 Gbps | ~125 MB/s | ~8 sec |
Actual speeds are typically 60–80% of advertised due to network overhead, congestion, and protocol efficiency. Use the File Size Download Calculator for precise estimates.
| File Type | Typical Size | Per GB |
|---|---|---|
| Text email | 5–20 KB | 50,000–200,000 |
| MP3 song (3 min) | 3–5 MB | 200–330 |
| JPEG photo (smartphone) | 3–5 MB | 200–330 |
| RAW photo (DSLR) | 25–50 MB | 20–40 |
| 1 min 1080p video | 130–175 MB | 6–8 min |
| 1 min 4K video | 350–400 MB | 2.5–3 min |
| eBook | 1–5 MB | 200–1,000 |
| AAA video game | 50–150 GB | N/A |
Convert any data storage unit. Use the free Data Storage Converter for unit conversions and the File Size Download Calculator for transfer time estimates — no signup required.
Related tools: Data Storage Converter · File Size Download Calculator · Bandwidth Calculator