Which unit does my OS use?

Windows: binary, but labels it "KB/MB/GB" without the "i". macOS since 10.6: actual decimal ("KB/MB/GB" = 1000-base). Linux: depends on the tool — `ls -l` in bytes, `ls -lh` binary, `du -h` same.

For file uploads, which unit counts?

Usually decimal on the server side (10 MB limit = 10,000,000 bytes). OS may show it as 9.5 MiB. To avoid surprises, leave 10% headroom.

Is 1 byte always 8 bits?

Yes, in modern standards. Historically there were 6, 7, 9-bit bytes. Since 1980 all systems use 8 bits/byte (octet). The term "octet" is used when there's ambiguity.

Why is 4K video so large?

4K = 4× the pixels of Full HD = 4× the data per frame. At 60fps, that's ~500 MB/min uncompressed. With modern codecs (H.265, AV1), it drops to 60-100 MB/min — still 5× larger than 1080p.

Does the BlipFiles converter use decimal or binary?

Binary (KB = 1024 B), which matches what operating systems display. For decimal contexts (physical drive, internet), divide the result by ~7.4% for GB or ~10% for TB.

Tutorial · unitConverter

File size units: KB, MB, GB and why they matter

You bought a "1 TB" SSD and the system shows 931 GB. The vendor isn't lying — it's binary vs decimal math. Here's the difference, plus a converter to settle it.

4 min readUpdated on April 27, 2026

There are TWO ways to measure file size, and they give different results for the same amount. This causes constant confusion: "my 1 TB drive shows 931 GB", "the 100 MB video became 95 MB after upload". Not a bug — it's a poorly-standardized convention.

Decimal vs Binary

Decimal (base 10): 1 KB = 1,000 bytes. 1 MB = 1,000,000 bytes. Like the rest of the metric system (km, kg). SI standard. Used by HDD/SSD makers, ISPs, network standards.

Binary (base 2, "kibi/mebi/gibi"): 1 KiB = 1,024 bytes. 1 MiB = 1,048,576 bytes. More natural for computers that think in powers of 2. Used by operating systems, RAM, file systems.

1 KB (decimal) = 1,000 bytes
1 KiB (binary) = 1,024 bytes
1 MB (decimal) = 1,000,000 bytes
1 MiB (binary) = 1,048,576 bytes
1 GB (decimal) = 1,000,000,000 bytes
1 GiB (binary) = 1,073,741,824 bytes (~7.4% larger)
1 TB (decimal) = 1,000,000,000,000 bytes
1 TiB (binary) = 1,099,511,627,776 bytes (~10% larger)

When each one matters

Email attachments

Email limits are usually decimal (Gmail = 25 MB = 25,000,000 bytes). But the file system shows MiB. A file that shows as 24 MiB can be 25.17 MB decimal — and Gmail rejects it. Safety margin: compress under 22 MB displayed.

Buying internet plans

Internet speed is measured in Megabits per second (Mbps), NOT MegaBytes (MBps). 8 Mbps = 1 MBps. "100 mega internet" = 100 Mbps = 12.5 MBps actual max download. That's why downloading 1 GB on a 100 Mbps plan takes ~80 seconds.

Buying HDD/SSD

Manufacturer uses decimal (sells more). OS shows binary. A "1 TB" SSD always becomes ~931 GB visible. Not fraud, just industry convention. Account for it when calculating needed space.

Typical reference sizes

Mobile JPG photo (12MP, high quality): 4-6 MB
PNG screenshot (Full HD): 200-500 KB
PDF 10 pages (text): 80-200 KB
Scanned PDF 10 pages: 5-15 MB
MP3 song (3 min, 320 kbps): 7 MB
1080p video (1 minute, mid quality): 50-100 MB
4K video (1 minute): 350-500 MB
Full 1080p movie: 1.5-3 GB
Average desktop app: 100-500 MB
Operating system (install): 4-15 GB

Pixels, dpi, and physical size

For print and design, you need to convert between pixels and physical units (mm, cm, in). The rule: 1 inch = 96 pixels on the web (CSS standard) or 300 dpi for quality print. 1 in = 25.4 mm.

A4 (210×297 mm) at 300 dpi = 2480×3508 px
A4 at 96 dpi (web) = 794×1123 px
Business card (90×50 mm) at 300 dpi = 1063×591 px
Instagram banner (1080×1080 px) at 96 dpi = ~286×286 mm equivalent

Frequently asked questions

Because the industry never standardized. IEC created KiB/MiB/GiB in 1998 to fix it, but Microsoft and others kept using "KB/MB/GB" for binary. Apple moved to decimal in 10.6 (2009). Linux usually shows both.

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