What is a data size?
Digital information is stored in bits (binary digits, 0 or 1) and bytes (8 bits). Everything on a computer — a photo, a song, a document — is a count of bytes. Because byte counts grow huge fast, we use prefixes: kilobyte, megabyte, gigabyte, terabyte, petabyte. The catch is that "kilo" can mean either 1000 (decimal, SI) or 1024 (binary, IEC). This single ambiguity causes endless confusion, so our data size converter lets you pick the convention.
Decimal vs binary — the core choice
In decimal notation, each step is 1000×: 1 KB = 1000 bytes, 1 MB = 1,000,000 bytes, 1 GB = 10⁹ bytes, 1 TB = 10¹², 1 PB = 10¹⁵. Hard-drive and SSD manufacturers, network speeds, and most international standards use this. In binary notation, each step is 1024× (2¹⁰): 1 KiB = 1024 bytes, 1 MiB = 1,048,576, 1 GiB = 1,073,741,824, and so on. RAM and many operating systems report capacity this way. The toggle at the top of the tool switches between them instantly.
The base-unit method
We convert your "from" value into bytes (the base unit) using the active notation, then divide by the target unit's byte factor. This works for any pair and stays exact to six decimals. For instance, in decimal mode 1 MB = 1,000,000 bytes and 1 GB = 1,000,000,000 bytes, so 1 MB = 0.001 GB. Flip to binary and 1 MiB = 1,048,576 bytes, 1 GiB = 1,073,741,824 bytes, so 1 MiB = 0.0009765625 GiB.
Key conversion factors
- 1 bit = 0.125 byte (8 bits = 1 byte, fixed)
- 1 byte = 1 B (the base)
- KB: 1000 (decimal) or 1024 (binary)
- MB: 1,000,000 or 1,048,576
- GB: 1,000,000,000 or 1,073,741,824
- TB: 1,000,000,000,000 or 1,099,511,627,776
- PB: 1,000,000,000,000,000 or 1,125,899,906,842,624
Why your drive looks smaller
A "1 TB" hard drive is marketed as 1,000,000,000,000 bytes (decimal). But Windows displays capacity in binary units, where 1 TiB = 1,099,511,627,776 bytes. Dividing 10¹² by that gives about 0.9095 TiB, which Windows labels "931 GB." Nothing was stolen — the drive honestly contains a trillion bytes; the OS just counts in 1024-based chunks. Our converter reproduces both views so you can see exactly where the "missing" space went.
Real-world examples
A typical MP3 song is ~4 MB (decimal) = 4,000,000 bytes. A 1080p movie might be 2.5 GB = 2,500,000,000 bytes. A modern laptop has 16 GB of RAM = 16 × 1,073,741,824 ≈ 17.2 billion bytes in binary terms. Cloud providers bill in decimal TB/PB. A fiber line at "1 Gbps" moves 1,000,000,000 bits per second = 125,000,000 bytes/s = 125 MB/s. Switching notation changes every one of these numbers, so choose deliberately.
Common mistakes
The biggest mistake is assuming KB always means 1024. In storage specs it means 1000; only memory contexts reliably mean 1024 (and strictly should be written KiB). Mixing the two inflates or shrinks figures by ~2.4% per step — ~7% from KB to GB, ~10% to TB. Also note 8 bits = 1 byte is constant: converting bits to bytes always divides by 8 regardless of mode. Finally, bandwidth (Mbps) is decimal bits, while file sizes are decimal or binary bytes — keep units straight when estimating download time.
Frequently asked questions
Base unit for data size?
The byte. All units convert to bytes first, then to the target.
Decimal or binary?
Storage/network: decimal (×1000). RAM/OS: binary (×1024). Toggle to match.
Bits in a byte?
8 bits = 1 byte, fixed in both modes.
Why is 1 TB drive ~931 GB?
Makers use decimal TB (10¹² B); Windows shows binary TiB, so 1 TB ≈ 0.9095 TiB ≈ 931 GiB.
What is a petabyte?
Decimal 10¹⁵ bytes; binary PiB ≈ 1.1259 × 10¹⁵ bytes. Used for big data.