Buy a "1 TB" drive and your computer reports something like 931 GB. Download a "5 MB" file and it isn't exactly 5 million bytes. These mismatches aren't errors — they come from two different ways of counting digital storage. Here's how the units actually work.
The building block: the byte
Everything starts with the bit (a single 0 or 1) and the byte (8 bits). One byte can store a single character like the letter "A." From there, sizes scale up through kilobytes, megabytes, gigabytes, and terabytes — but the multiplier depends on whether you're counting in decimal or binary.
Decimal vs. binary: 1000 vs. 1024
There are two competing standards:
- Decimal (SI): 1 KB = 1,000 bytes, 1 MB = 1,000 KB, and so on. Storage manufacturers use this.
- Binary: 1 KiB = 1,024 bytes, 1 MiB = 1,024 KiB. Operating systems often use this but label it "KB/MB."
The common convention you'll see in everyday software is 1 KB ≈ 1,024 bytes, with 1 MB = 1,024 KB and 1 GB = 1,024 MB. That 24-byte gap per kilobyte compounds at every level.
| Unit | Decimal (×1000) | Binary (×1024) |
|---|---|---|
| 1 KB / KiB | 1,000 bytes | 1,024 bytes |
| 1 MB / MiB | 1,000,000 | 1,048,576 |
| 1 GB / GiB | 1,000,000,000 | 1,073,741,824 |
| 1 TB / TiB | 1,000,000,000,000 | 1,099,511,627,776 |
Why your drive looks smaller
This table explains the "missing" storage. A drive sold as 1 TB holds 1,000,000,000,000 bytes (decimal). Your OS divides by 1,073,741,824 to show gigabytes the binary way, giving about 931 GB. No space vanished — the two sides just counted differently.
The same gap explains why a file shown as "1.0 MB" might be 1,048,576 bytes on disk rather than an even million. When precision matters — checking upload limits, email attachment caps, or backup capacity — it pays to know which convention a tool is using.
How to use it
Rather than memorizing these multipliers, let the File Size Converter do the math. Enter a value in any unit and see bytes, KB, MB, GB, and TB all at once, so you can instantly tell whether a file fits a 25 MB email cap or a 2 GB upload limit.
File sizes are ultimately a base-2 story, since 1,024 is 2 to the 10th power. If you're curious how binary powers produce these neat numbers, the Number Base Converter makes the relationship between binary and decimal click. And for everyday measurements outside the digital world, the Unit Converter handles length, weight, and temperature with the same one-tap simplicity.