File Size Converter

Why File Sizes Are Confusing

You've seen this: your hard drive is rated for 1 TB, but your operating system shows 931 GB available. Your internet plan is 100 Mbps, but downloads top out around 12 MB/s. Your email allows 25 MB attachments, but the client's file is 18,432 KB and you have no idea if that's over the limit without doing arithmetic.

These conversions trip people up because they involve two different things that look the same: bits vs. bytes, and the sneaky confusion between decimal (1 KB = 1,000 bytes, used by storage manufacturers) vs binary (1 KB = 1,024 bytes, used by operating systems).

This tool gives you all conversions at once so you never have to do that math in your head again.

The Unit Scale Explained

Starting from the smallest meaningful unit:

The Binary vs. Decimal Confusion (Why Your Drive Shows Less Than Advertised)

This is the most commonly misunderstood aspect of file sizes.

Hard drive manufacturers market storage using decimal prefixes: 1 TB = exactly 1,000,000,000,000 bytes. It's clean marketing math.

Windows traditionally reports storage in binary units: 1 "GB" in Windows = 1,073,741,824 bytes (2^30). So when Windows sees a 1 TB drive, it calculates: 1,000,000,000,000 ÷ 1,073,741,824 ≈ 931 GB.

The drive isn't missing space. It's a units mismatch. The technically correct term for the binary version is gibibyte (GiB) vs. gigabyte (GB), a distinction the IEC standardized in 1998 — but most people (and most software) still use GB loosely for both.

This tool uses the binary (1,024-based) standard — which matches what your OS shows.

Practical Use Cases

Planning storage: How many iPhone photos fit on a 128 GB memory card if each photo averages 4 MB? (128 GB = 131,072 MB; 131,072 ÷ 4 = ~32,768 photos)

Checking email attachments: Your limit is 25 MB. The file you want to send is 18,450 KB. Is it under the limit? (18,450 KB ÷ 1,024 = 18.02 MB — just fits)

Figuring out download time: Your plan is 100 Mbps. How long will a 4 GB game update take? (4 GB = 4,096 MB = 32,768 Mb; 32,768 ÷ 100 = 327.68 seconds ≈ 5.5 minutes)

Comparing cloud storage plans: Is 100 GB enough for your project files? Convert your current folder size from bytes to GB and compare directly.

Mobile data planning: If you stream video at 1.5 GB/hour and have 5 GB of mobile data left, you have roughly 3.3 hours of streaming.

The One Thing People Always Forget

Network speeds use bits, file sizes use bytes.

Internet plan: 100 Mbps = 100 Megabits per second
Actual download speed: 100 ÷ 8 = 12.5 MB/s (Megabytes per second)

This is why a "100 Mbps" broadband plan doesn't download at 100 MB/s. Always divide by 8 when converting a speed in Mbps to a download rate in MB/s.

Limitations

The converter uses binary (base-1024) prefixes, matching traditional OS behavior. This will give you slightly different results from tools that use decimal (base-1000) prefixes (which match manufacturer specs). Neither is wrong — they use different conventions. If you're comparing against a storage manufacturer's spec sheet, their number uses 1,000-based units.

Frequently Asked Questions

Why does my 500 GB hard drive show as 465 GB in Windows? Same reason as above: binary vs. decimal units. 500,000,000,000 bytes ÷ 1,073,741,824 = 465.66 GiB. Windows shows gibibytes but labels them "GB."

Is there a difference between Mb and MB? Yes — and it matters. Lowercase b = bits. Uppercase B = bytes. Mb = Megabits; MB = Megabytes. Internet speeds are always in Megabits (Mbps). File sizes are always in Megabytes (MB).

What is a Petabyte? Does it apply to me? A Petabyte (1,024 TB) is used by cloud platforms, streaming services, and large enterprises. If Facebook or YouTube talks about the amount of data they store, they measure in petabytes or exabytes. For personal use, you'll rarely deal with anything beyond terabytes.