Data Storage Units Explained: KB, MB, GB, TB & Beyond
Updated: July 2026
Phone storage, internet speeds and hard drives all use data units — but bits, bytes and the two competing definitions of "kilo" confuse almost everyone. This guide untangles them with practical examples.
Bits vs bytes: the crucial difference
A bit is a single binary digit (0 or 1). A byte is 8 bits. Internet speeds are sold in bits per second (Mbps), while files are measured in bytes (MB). That is why a "100 Mbps" connection downloads at roughly 12.5 MB per second — divide by 8.
The ladder of units
- 1 kilobyte (KB) = 1,000 bytes — a short email
- 1 megabyte (MB) = 1,000 KB — a minute of MP3 audio
- 1 gigabyte (GB) = 1,000 MB — about 250 songs or an hour of HD video
- 1 terabyte (TB) = 1,000 GB — roughly 250,000 photos
Why your 1 TB drive shows 931 GB
Manufacturers use decimal units (1 TB = 1,000,000,000,000 bytes), but operating systems often measure in binary units (1 TiB = 1,099,511,627,776 bytes). The missing space is not gone — it is the same number of bytes displayed on two different scales. 1 TB decimal ≈ 0.909 TiB binary, hence "931 GB".
Practical rules of thumb
To convert Mbps to MB/s, divide by 8. To estimate download time, divide file size (MB) by speed (MB/s). A 4.5 GB movie on a 50 Mbps line: 4,500 MB ÷ 6.25 MB/s ≈ 12 minutes. For storage planning, photos average 3-5 MB, an hour of 4K video runs 20-40 GB.
Frequently asked questions
Why does my internet download slower than advertised?
Speeds are sold in megabits per second (Mbps) but files show in megabytes (MB). Divide the advertised speed by 8: a 100 Mbps plan gives at most 12.5 MB/s, before network overhead.
Why does a 1 TB drive show only 931 GB?
The drive contains a full trillion bytes, but your operating system displays capacity using binary units (1,024-based). The same bytes read as 931 "gigabytes" on that scale — nothing is missing.
How many photos fit in a gigabyte?
Around 200-330 smartphone photos at typical 3-5 MB each. RAW photos from dedicated cameras are far larger, often 25-50 MB, so only 20-40 per gigabyte.