How to Convert Data Storage: MB, GB, TB, Binary vs Decimal Explained
Decimal gigabytes (1,000 MB) vs binary gibibytes (1,024 MiB), hard drive capacity discrepancies, and file transfer math.
The 1000 vs 1024 Discrepancy (Why Your New Hard Drive Seems “Smaller”)
Have you ever purchased a brand-new 1 Terabyte (1 TB) hard drive or SSD, plugged it into a Windows computer, and discovered to your dismay that it only reports 931 GB of free space? Where did the missing 69 gigabytes go?
Your drive is not broken, and no storage was stolen. The discrepancy stems from two competing mathematical standards for measuring digital bytes: Decimal (SI base-10) versus Binary (IEC base-2).
Decimal (SI) vs. Binary (IEC) Prefixes
Storage manufacturers measure drives using standard decimal prefixes, while operating systems like Microsoft Windows measure memory using powers of 2:
| Prefix | Decimal Standard (SI Base-10) | Binary Standard (IEC Base-2) | Discrepancy |
|---|---|---|---|
| Kilo / Kibi | 1 KB = 1,000 Bytes | 1 KiB = 1,024 Bytes | +2.4% |
| Mega / Mebi | 1 MB = 1,000,000 Bytes | 1 MiB = 1,048,576 Bytes | +4.9% |
| Giga / Gibi | 1 GB = 1,000,000,000 Bytes | 1 GiB = 1,073,741,824 Bytes | +7.4% |
| Tera / Tebi | 1 TB = 1,000,000,000,000 Bytes | 1 TiB = 1,099,511,627,776 Bytes | +9.9% |
The Math Behind the Missing 69 Gigabytes
When hard drive manufacturers sell a 1 TB drive, it contains exactly 1,000,000,000,000 bytes. But Windows divides that byte count by 1,024 three times (bytes → KiB → MiB → GiB):
Windows displays “931 GB” (using the GB abbreviation while actually measuring in GiB), creating the illusion of missing capacity.
Bits vs. Bytes (Internet Speed vs. File Size)
Another common point of confusion is internet speed vs. file download time:
- Lowercase “b” = Bits: Used for transmission speeds (e.g. 100 Mbps = 100 megabits per second).
- Uppercase “B” = Bytes: Used for file sizes (1 Byte = 8 bits).
- To convert internet speed into download capability, divide by 8: A 100 Mbps internet connection downloads at a maximum theoretical rate of
100 / 8 = 12.5 Megabytes per second (MB/s).
Worked Example: Estimating Download Times
How long does it take to download a 15 GB video game update over a 50 Mbps broadband connection?
- Convert file size to Megabytes: 15 GB × 1,000 = 15,000 MB.
- Convert internet speed to MB/s: 50 Mbps ÷ 8 = 6.25 MB/s.
- Divide file size by speed: 15,000 MB ÷ 6.25 MB/s = 2,400 seconds.
- Convert to minutes: 2,400 ÷ 60 = 40 minutes.
Convert Data Storage Units Instantly
Switch seamlessly between decimal and binary digital units with our client-side tool:
- Convert bytes, KB, MB, GB, and TB with our Data Storage Converter.
- Check password entropy and key bit strength with our Password Generator.
- Explore all converter tools on the Unit Converters Hub.
Put This Into Practice
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