File Size Converter — KB, MB, GB & KiB, MiB, GiB

How the File Size Converter Works

Enter any value, select its unit, and all 9 units update simultaneously. The tool never rounds the intermediate bytes value, it converts to exact bytes first, then divides by the target unit's factor. This means you see the full precision of each conversion.

SI units (KB, MB, GB, TB) — use powers of 1,000. 1 KB = 1,000 bytes. Used by storage manufacturers and network specs.
IEC units (KiB, MiB, GiB, TiB) — use powers of 1,024. 1 KiB = 1,024 bytes. Used by operating systems internally. Defined in IEC 60027-2.

The IEC Standard and Why It Matters

The IEC 60027-2 standard (published 1998, updated 2000) introduced binary prefixes — kibi, mebi, gibi, tebi — precisely to end the ambiguity between powers-of-1000 and powers-of-1024 unit names. Before this standard, "kilobyte" was ambiguous: it sometimes meant 1,000 bytes (SI) and sometimes 1,024 bytes (computing). The confusion is especially visible at larger scales: a "1 TB" hard drive advertised by a manufacturer holds 1,000,000,000,000 bytes (SI). Windows reports this as roughly 931 GiB (IEC) because the OS divides by 1,024³, not 1,000³. No data is missing, it is purely a labeling difference.

In practice: network speeds (Mbps, Gbps) always use SI (powers of 1,000). RAM is traditionally sold and reported in IEC binary multiples. SSD and HDD manufacturers use SI. macOS switched from IEC to SI reporting in macOS 10.6 (Snow Leopard, 2009), so it now agrees with the label on the box. Linux and Windows still report in IEC.

All 9 units, one grid, copy on click

Most file size tools show you one result at a time. This one shows all 9 simultaneously — 5 SI and 4 IEC — in two clearly labelled sections. Click any unit card to copy the value and unit to your clipboard. The active input unit is highlighted so you always know which direction you started from.

What isn't here: a file size estimator for images (which depends on format, bit depth, and compression), network transfer time calculations, or storage cost calculators. Those require additional inputs and belong in separate tools.

Binary (GiB) vs Decimal (GB): Why the Confusion?

Two competing systems define file size units, and both are in active use today:

Decimal (SI): 1 KB = 1,000 bytes, 1 MB = 1,000,000 bytes, 1 GB = 1,000,000,000 bytes. Used by storage manufacturers (HDD, SSD, USB drives) to advertise capacity.
Binary (IEC): 1 KiB = 1,024 bytes, 1 MiB = 1,048,576 bytes, 1 GiB = 1,073,741,824 bytes. Used by operating systems (Windows, macOS, Linux) to report file sizes and storage.
The confusion: a "1 TB" hard drive marketed by the manufacturer contains 1,000,000,000,000 bytes. Windows shows it as ~931 GB (1,000,000,000,000 ÷ 1,073,741,824). macOS (since Monterey) shows it as 1 TB using decimal. This causes the "missing storage" confusion.
IEC standard (2000): officially named kibibyte (KiB), mebibyte (MiB), gibibyte (GiB), tebibyte (TiB). Most people still say "gigabyte" for both — context determines which is meant.

Practical File Size Benchmarks

Putting file sizes in context helps you understand storage and transfer at a glance:

1 KB: a short text email; a simple HTML page
1 MB: a 1-minute MP3 at 128 kbps; a low-resolution JPEG photo; a 100-page plain text document
10 MB: a typical smartphone photo (JPEG, high quality); a 10-minute podcast episode
100 MB: a short HD video clip (2–3 minutes); a medium-sized mobile app
1 GB: a 90-minute HD movie (streaming quality); a large mobile game; ~1,000 typical smartphone photos
1 TB: ~250,000 HD photos; ~500 HD movies; typical modern laptop SSD capacity

Internet speed context: a 100 Mbps connection downloads at 12.5 MB/s. A 4K Netflix stream uses ~25 Mbps (~3 MB/s), which equals 10.8 GB per hour of viewing.

Frequently Asked Questions

Why does my 1 TB hard drive show as 931 GB in Windows?

The manufacturer labels it as 1 TB using SI (1,000,000,000,000 bytes). Windows reports in GiB (IEC), dividing by 1,024³ = 1,073,741,824 bytes, which gives 931.32 GiB. No data is missing, it is purely a labeling difference between SI and IEC conventions.

What is the difference between GB and GiB?

GB (gigabyte, SI) = 1,000,000,000 bytes. GiB (gibibyte, IEC) = 1,073,741,824 bytes. The difference is about 7.4%. The IEC binary prefixes (KiB, MiB, GiB, TiB) were introduced by IEC standard 60027-2 to eliminate this ambiguity.

Are network speeds in SI or IEC?

Network speeds (Mbps, Gbps) always use SI — powers of 1,000. A 100 Mbps connection transfers 100,000,000 bits per second, or 12,500,000 bytes per second (12.5 MB/s SI). This is why downloading a 1 GB file on a 100 Mbps line takes about 80 seconds, not 71 seconds.

Which operating systems use IEC vs SI?

Windows and Linux report file sizes in IEC binary units (GiB) but label them as 'GB', which is technically incorrect. macOS switched to correct SI labeling in Snow Leopard (2009), so a 1 TB drive shows as ~1 TB in macOS but ~931 GB in Windows.

What standard defines binary prefixes?

IEC 60027-2 (International Electrotechnical Commission), first published in 1998 and updated in 2000. It defines kibi (2¹⁰), mebi (2²⁰), gibi (2³⁰), and tebi (2⁴⁰) prefixes to unambiguously represent powers of 1,024.

Why does my 1 TB hard drive show less space than 1 TB?

Storage manufacturers use decimal gigabytes (1 GB = 1,000,000,000 bytes). Operating systems report space in binary gibibytes (1 GiB = 1,073,741,824 bytes). A 1 TB drive contains 1,000,000,000,000 bytes, which equals ~931 GiB — what Windows displays as ~931 GB. You haven't lost any space; it's a unit labeling difference. macOS switched to decimal reporting in Monterey, so it shows the full 1 TB.

What is a megabit vs a megabyte?

1 byte = 8 bits. Internet speeds are measured in megabits per second (Mbps); file sizes are measured in megabytes (MB). To convert Mbps to MB/s download speed, divide by 8: a 100 Mbps connection downloads at 12.5 MB/s. A 100 MB file at 100 Mbps takes about 8 seconds to download (100 MB × 8 bits ÷ 100 Mbps = 8 seconds).

By Bam's Thinkery — Updated May 2, 2026