Data Storage Converter: Bytes, KB, MB, GB, TB Explained

Data storage measurement involves two distinct systems—binary and decimal—that create persistent confusion about actual storage capacity. Understanding these systems resolves the common discrepancy between advertised and usable storage space.

My buddy Tom, a video editor, once bought a spankin' new 4 TB external drive for his workstation. Plugged it in, and Windows showed 3.63 TB. He was fuming — thought he'd been ripped off. Called the manufacturer, threatened a chargeback, the whole nine yards. Turns out, his drive was fine. He just didn't know that drive makers use decimal (1 TB = 1,000,000,000,000 bytes) while Windows reports in binary dressed up as decimal. A quick explanation saved him a world of hassle. These days he tells every newbie editor he mentors: "Know your gibibytes from your gigabytes before you buy."

Photo by Nick on Unsplash

Binary versus Decimal Prefixes

Here's the rub. Both camps use the same words — kilobyte, megabyte, gigabyte — but they mean different things. It's like saying "foot" in America versus "foot" in England: same word, different lengths.

Decimal (SI) prefixes run on base-10. Nice and tidy, powers of 1,000:

• Kilobyte (KB) = 1,000 bytes


• Megabyte (MB) = 1,000 KB = 1,000,000 bytes


• Gigabyte (GB) = 1,000 MB = 1,000,000,000 bytes


• Terabyte (TB) = 1,000 GB = 1,000,000,000,000 bytes

Binary (IEC) prefixes run on base-2. Powers of 1,024 instead:

• Kibibyte (KiB) = 1,024 bytes


• Mebibyte (MiB) = 1,024 KiB = 1,048,576 bytes


• Gibibyte (GiB) = 1,024 MiB = 1,073,741,824 bytes


• Tebibyte (TiB) = 1,024 GiB = 1,099,511,627,776 bytes

Notice the pattern? Drive makers use decimal. Windows uses binary — but slaps decimal labels on it. That's why your 1 TB drive shows up as a measly 931 GB. It's not a scam. It's a units fight nobody bothered to settle.

Storage History

We've come a long way from the IBM 350 RAMAC in 1956 — that beast stored 5 million characters on 50 spinning disks and weighed more than a car. Now I carry terabytes in my pocket. Go figure.

Floppy disks ruled the roost for decades. First 8-inch (80 KB), then 5.25-inch (360 KB), finally 3.5-inch (1.44 MB). That's smaller than a single JPEG today. Then came CDs (700 MB), DVDs (4.7 GB), and Blu-rays (up to 128 GB). Flash memory? It went from barely holding a text file to USB drives that laugh at a terabyte.

These days your laptop's SSD can hit 4-8 TB, and enterprise HDDs? They're pushing past 20 TB. Storage isn't the bottleneck anymore.

Why 1TB = 931GB on Drives

Now you know the dirty secret: your drive's 1,000,000,000,000 bytes (decimal TB) gets divided by 1,073,741,824 (binary GiB conversion). That gives you 931.32 GiB. Your OS calls it "931 GB" because it's using the wrong label. The IEC tried to fix this back in 1998 with proper names — kibibyte, mebibyte, gibibyte — but old habits die hard.

Common File Sizes

To wrap your head around what all those bytes actually mean:

• Text document: 50 KB — barely a blip


• Digital photo (JPEG): 2-5 MB


• MP3 song (320kbps): 5-10 MB


• HD video (1 hour): 1-3 GB — yes, that much


• 4K video (1 hour): 7-14 GB


• Modern video game: 50-150 GB — some are pushing 200+


• Operating system installation: 20-64 GB

See the pattern? Everything's getting hungrier for space.

Practical Conversion

Quick rule of thumb: hardware specs use decimal (divide by 1,000). What your OS actually shows? Binary dressed as decimal (divide by 1,024). Know the difference, and you'll never freak out about "missing" space again — unlike Tom, who nearly had a meltdown over his 3.63 TB "4 TB" drive.