How Big Is a Megabyte vs a Gigabyte?
A gigabyte is a thousand megabytes, which is a thousand kilobytes. What each holds in photos, songs and video, and why your 1 TB drive shows as 931 GB.
In short
A kilobyte is a thousand bytes, a megabyte a thousand kilobytes, a gigabyte a thousand megabytes and a terabyte a thousand gigabytes, each step a thousand times larger. A megabyte holds roughly a minute of MP3 audio or a small photo; a gigabyte holds about 250 phone photos or an hour of standard-definition video; a terabyte holds around a thousand hours of it.
The units are simple, they climb in steps of a thousand, and almost every confusion about them comes from two things: the difference between bits and bytes, and the difference between a thousand and 1,024.
The ladder
| Unit | Bytes | Roughly holds |
|---|---|---|
| Byte | 1 | One character of text |
| Kilobyte (KB) | 1,000 | A short email, half a page of text |
| Megabyte (MB) | 1,000,000 | A minute of MP3, a small photo |
| Gigabyte (GB) | 1,000,000,000 | 250 phone photos, an hour of SD video |
| Terabyte (TB) | 1,000,000,000,000 | 250,000 photos, a thousand hours of SD video |
Each step is a thousand times the last, which means a terabyte is a million megabytes, and it means intuition about the gap between them fails in exactly the way it fails for million and billion.
Everyday sizes
- A text message: under 1 KB
- A web page: 2 to 5 MB with images and scripts
- A phone photo: 3 to 6 MB
- A three-minute song as MP3: about 3 to 4 MB
- A high-resolution photo from a camera: 20 to 30 MB
- A one-hour HD video download: 1 to 3 GB
- A modern game: 50 to 150 GB
- A phone’s storage: 128 to 512 GB
- A laptop drive: 256 GB to 2 TB
Bits versus bytes
A bit is a single 1 or 0. A byte is eight bits. Storage is measured in bytes; network speed is measured in bits per second. The abbreviations differ by case: MB is megabytes, Mb is megabits.
A 100 Mbps broadband line moves 100 megabits a second, which is 12.5 megabytes a second. A 1 GB file therefore takes about 80 seconds at full speed, not 10. This single conversion explains most of the gap between advertised speed and experienced download time.
The 1,024 problem
Computers work in binary, and 2 to the power of 10 is 1,024, which is close enough to 1,000 that early computing used “kilobyte” for both. That ambiguity never went away.
Drive manufacturers use the decimal definition: 1 TB is exactly one trillion bytes. Windows, and historically most operating systems, report in binary units: 1 “TB” on screen is 1,099,511,627,776 bytes. Divide one trillion by that and you get 0.909, so a 1 TB drive appears as 931 GB.
The formal fix was to name the binary units kibibyte, mebibyte, gibibyte and tebibyte, with the abbreviations KiB, MiB, GiB and TiB. macOS and most Linux systems now report in decimal, matching the box. Windows still uses binary but labels it GB. Nothing is lost either way; the two sides are counting in different units.
Streaming and data allowances
Video dominates data use. Standard definition streams at roughly 1 GB an hour, HD at about 3 GB, and 4K at 7 GB or more. A 20 GB monthly mobile allowance is therefore about six hours of HD video, or well over a hundred hours of music. Knowing that is the quickest way to work out which activity is actually eating the allowance.
Common questions
Why does my 1 TB drive show 931 GB?
Manufacturers count a terabyte as a trillion bytes. Operating systems have historically counted in powers of two, where a terabyte is 1,099,511,627,776 bytes. A trillion bytes divided by that is 0.909, so the drive shows 931 of those larger units. Nothing is missing; the two sides count differently.
Is a megabit the same as a megabyte?
No. A byte is eight bits. Broadband speeds are quoted in megabits per second, file sizes in megabytes, so a 100 Mbps connection downloads at most 12.5 megabytes a second. This is why downloads seem slower than the advertised speed.
How much data does streaming use?
Roughly 1 GB an hour for standard definition, 3 GB for high definition, and 7 GB or more for 4K. Music streaming uses around 50 to 150 MB an hour depending on quality.
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