File Size Converter – KB, MB, GB, TB Converter

Unit	Value
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File Sizes Explained: Bytes, Kilobytes, Megabytes, and the Binary vs. Decimal Divide

A byte is the foundational unit of digital storage — 8 bits, enough to represent one character of ASCII text. Everything above a byte is just a multiplied prefix, but there are two competing systems that use nearly identical names for different values. The decimal (SI) system defines a kilobyte as exactly 1,000 bytes, a megabyte as 1,000,000 bytes, and so on — powers of 10. The binary (IEC) system, which reflects how computer memory is actually addressed, defines a kibibyte (KiB) as 1,024 bytes, a mebibyte (MiB) as 1,048,576 bytes — powers of 2. The 2.4% difference per step compounds quickly: by the time you reach gigabytes, a "GB" by decimal measure is about 7.4% smaller than a "GiB" by binary measure.

This discrepancy explains a common frustration: you buy a 1 TB hard drive, but Windows shows it as 931 GB. The drive manufacturer uses decimal (1 TB = 1,000,000,000,000 bytes), while Windows historically reports in binary gibibytes without using the correct "GiB" label — it just calls them "GB." macOS switched to using decimal gigabytes in OS X 10.6, so a 1 TB drive shows as 1.00 TB on a Mac. Neither measurement is wrong — they just use different definitions of the same word. This converter shows both systems simultaneously so you can see exactly what each value means.

Unit	Symbol	Size	Typical Use
Byte	B	8 bits	Single character, smallest addressable unit
Kilobyte	KB	1,000 bytes	Small text files, email messages
Kibibyte	KiB	1,024 bytes	RAM addressing, OS memory reports
Megabyte	MB	1,000,000 bytes	Photos, songs, storage marketing
Mebibyte	MiB	1,048,576 bytes	Windows file properties, RAM sizing
Gigabyte	GB	1,000,000,000 bytes	Drive capacity, macOS file sizes
Gibibyte	GiB	1,073,741,824 bytes	Windows "GB" display (mislabeled)
Terabyte	TB	1,000,000,000,000 bytes	Hard drives, SSDs, cloud storage

Worked Examples

Example 1 — Why your 256 GB SSD shows less space
Your SSD is marketed as 256 GB (decimal: 256 × 10⁹ = 256,000,000,000 bytes). Windows reports capacity in binary GiB but labels them "GB": 256,000,000,000 ÷ 1,073,741,824 = 238.4 GiB. So Windows shows ~238 GB. Subtract 5–10 GB for the recovery partition and you have roughly 228 GB of usable space. No bytes were stolen — just two different counting systems.

Example 2 — Converting a 45 MB file to kilobytes
In decimal: 45 MB × 1,000 = 45,000 KB. In binary: 45 MB is first converted to bytes (45 × 1,000,000 = 45,000,000 bytes), then to KiB (45,000,000 ÷ 1,024 = 43,945.3 KiB). If you are uploading to a service with a "50,000 KB" limit, clarify whether it means decimal KB (50 MB) or binary KiB (~48.8 MB) — the difference can matter for large files.

Frequently Asked Questions

What is the difference between KB and KiB?

KB (kilobyte) in the SI/decimal system equals exactly 1,000 bytes. KiB (kibibyte) in the IEC binary system equals 1,024 bytes. The same ambiguity extends to all prefixes: MB vs MiB, GB vs GiB, TB vs TiB. Hard drive manufacturers use decimal; operating systems and RAM specs traditionally use binary. This converter shows both so you can compare directly.

Why does Windows report different file sizes than macOS?

Windows traditionally reports file and drive sizes in binary units (powers of 1,024) but labels them "KB", "MB", and "GB" — which are technically decimal prefixes. macOS switched to using decimal prefixes correctly starting with OS X Snow Leopard (10.6) in 2009. So a 1 GB file is 1,000,000,000 bytes on macOS but appears as 953 MB on Windows (because 1,000,000,000 ÷ 1,024³ ≈ 0.931 GiB, displayed as "GB").

What is a megabyte?

A megabyte (MB) is 1,000,000 bytes in the SI decimal system, or 10⁶ bytes. In practical terms, a 3-minute MP3 song is typically 3–5 MB, a 12-megapixel JPEG photo is 3–8 MB, and a 10-page Word document might be under 1 MB. The binary equivalent is the mebibyte (MiB) = 1,048,576 bytes — about 4.9% larger than a decimal megabyte.

How many MB are in a GB?

In the decimal system: exactly 1,000 MB in 1 GB (since both are powers of 10: 10⁹ ÷ 10⁶ = 10³). In the binary system: 1,024 MiB in 1 GiB (since 2³⁰ ÷ 2²⁰ = 2¹⁰ = 1,024). If you are comparing storage marketed in GB to a Windows size report in "GB" (which is actually GiB), 1 "Windows GB" = 1,024 "Windows MB" = 1,073.7 MB in decimal terms.

What are typical file sizes for common file types?

Text document (10 pages): 30–100 KB. JPEG photo (smartphone): 3–8 MB. RAW photo (DSLR): 20–45 MB. MP3 song (3 min): 3–5 MB. FLAC song (lossless): 20–40 MB. HD video (1 min at 1080p): 150–400 MB. 4K video (1 min): 700 MB–2 GB. Installed PC game: 10–150 GB. These vary widely with quality settings, compression, and content complexity.