Data Storage Converter
SI vs Binary Units
SI units (KB, MB, GB) use powers of 1000, while binary units (KiB, MiB, GiB) use powers of 1024. Operating systems often display sizes differently - Windows uses binary calculations but labels them with SI units.
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Understanding Data Storage Units
The Bit and Byte
A bit is the smallest unit of data, representing a single binary digit (0 or 1). A byte consists of 8 bits and can represent 256 different values (2^8). Most file sizes are measured in bytes or multiples of bytes.
SI Units (Decimal)
Kilobyte (KB)
1,000 bytes. About the size of a very short email or a few paragraphs of plain text.
Megabyte (MB)
1,000,000 bytes. A typical MP3 song is 3-5 MB. A high-resolution photo is 2-5 MB.
Gigabyte (GB)
1,000,000,000 bytes. A standard DVD holds about 4.7 GB. An HD movie is typically 4-8 GB.
Terabyte (TB)
1,000,000,000,000 bytes. Modern hard drives are 1-4 TB. About 500 hours of HD video.
Binary Units (IEC Standard)
Kibibyte (KiB)
1,024 bytes. Binary kilobyte used in computing. 2^10 bytes.
Mebibyte (MiB)
1,048,576 bytes. Binary megabyte. 2^20 bytes.
Gibibyte (GiB)
1,073,741,824 bytes. Binary gigabyte. 2^30 bytes.
Tebibyte (TiB)
1,099,511,627,776 bytes. Binary terabyte. 2^40 bytes.
SI vs Binary: The Confusion
Why Hard Drive Sizes Seem Wrong
Storage manufacturers use SI units (1 GB = 1,000,000,000 bytes), but operating systems like Windows historically used binary calculations while displaying SI labels.
Result: A "1 TB" drive shows as ~931 GB in Windows because Windows divides by 1,073,741,824 (GiB) instead of 1,000,000,000 (GB). The drive has exactly as many bytes as advertised - the labels are just interpreted differently.
Common File Sizes
| File Type | Typical Size |
|---|---|
| Plain text email | 1-5 KB |
| Word document (few pages) | 50-500 KB |
| MP3 song (4 min) | 3-5 MB |
| High-res photo (JPEG) | 2-10 MB |
| RAW photo | 25-50 MB |
| HD movie (1080p) | 4-8 GB |
| 4K movie | 15-30 GB |
Data Transfer vs Storage
Internet speeds are measured in bits per second (Mbps, Gbps), while file sizes are in bytes.
To convert: divide bits by 8 to get bytes. A 100 Mbps connection can theoretically download 12.5 MB per second (100 ÷ 8 = 12.5).
Frequently Asked Questions
Why does my 1TB hard drive show less space in Windows?
Storage manufacturers use decimal units (1 GB = 1,000,000,000 bytes), while Windows historically used binary calculations (1 GiB = 1,073,741,824 bytes) with decimal labels. So a '1 TB' drive (1,000,000,000,000 bytes) shows as ~931 GB in Windows. The drive has the advertised bytes—the display convention differs.
What's the difference between KB and KiB?
KB (kilobyte) uses the decimal definition: 1 KB = 1,000 bytes. KiB (kibibyte) uses the binary definition: 1 KiB = 1,024 bytes. The IEC introduced KiB/MiB/GiB in 1998 to clarify this confusion, though both terms are still used interchangeably in many contexts.
How do I convert MB to GB?
Using decimal (SI) units: divide MB by 1,000 to get GB. For example, 5,000 MB ÷ 1,000 = 5 GB. Using binary units: divide MiB by 1,024 to get GiB. For example, 5,120 MiB ÷ 1,024 = 5 GiB.
Why are internet speeds in Mbps but file sizes in MB?
Internet speeds are measured in bits per second (Mbps = megabits per second), while file sizes use bytes (MB = megabytes). Since 1 byte = 8 bits, divide Mbps by 8 to estimate MB/s download speed. A 100 Mbps connection can theoretically download about 12.5 MB per second.