A phone with “128 GB” of storage and a broadband plan advertising “100 Mbps” both use the same family of units, but a byte, a kilobyte, a megabyte, and a gigabyte scale up so quickly that it’s easy to lose track of just how much bigger each step really is.
Starting From the Byte
A single byte, 8 bits, is enough to store one character of text under the ASCII system — the letter “A”, a space, or a comma each take up one byte. On their own, individual bytes are far too small a unit to describe anything like a photo or a song, which is why storage is almost always measured in much larger multiples of the byte.
Kilobytes and Megabytes
A kilobyte (KB) is roughly a thousand bytes — enough for a short page of plain text. A megabyte (MB) is roughly a thousand kilobytes, or about a million bytes, which is closer to the size of a compressed photo or a few minutes of MP3 audio. Each step up multiplies the previous unit by about a thousand, which is why file sizes can look wildly different depending on which unit they’re expressed in.
Gigabytes and Beyond
A gigabyte (GB) is roughly a thousand megabytes, or about a billion bytes — the scale most people encounter when talking about phone storage, video files, or software installs. Beyond that sits the terabyte (TB), about a thousand gigabytes, which is the scale of modern external hard drives and cloud storage plans.
Why the Numbers Sometimes Don’t Match Up
Storage manufacturers and operating systems don’t always calculate these units the same way — manufacturers typically use 1,000 as the multiplier between units, while some operating systems use 1,024, which is why a drive advertised as “1 TB” often shows up as slightly less than 1,000 GB once it’s plugged in. Neither number is wrong; they’re just counting with a slightly different base.
The Units in a Table
- 1 byte = 8 bits
- 1 KB = 1,000 bytes (1,024 in some systems)
- 1 MB = 1,000 KB, or about 1 million bytes
- 1 GB = 1,000 MB, or about 1 billion bytes
- 1 TB = 1,000 GB, or about 1 trillion bytes
What Different Files Look Like
These are rough, typical sizes and they vary a lot by quality and format:
- A page of plain text: a few KB.
- A web-sized photo: a few hundred KB to a few MB.
- A song as an MP3: roughly 3 to 10 MB.
- A short HD video clip: tens to hundreds of MB.
- A full HD movie: usually several GB.
Why a Drive Shows Less Than Advertised
Drive makers count in powers of 1,000, while some operating systems count in powers of 1,024 (which is formally called a gibibyte, or GiB). A 128 GB phone has 128,000,000,000 bytes, and dividing that by 1,073,741,824 gives about 119.2 GiB. A 1 TB drive holds 1,000,000,000,000 bytes, which is about 931 GiB. Part of the difference is also used by the system itself.
KB vs KiB
To remove the confusion, standards bodies introduced separate names for the 1,024-based units: KiB, MiB, GiB and TiB. The “i” means binary. You will see them in technical software, while everyday products still use KB, MB and GB.
Download Time Example
A 1 GB file is 8,000 megabits. On a 100 Mbps connection, the best-case time is 8,000 divided by 100, or 80 seconds. Real downloads are slower because of overhead and shared bandwidth. Remember that speeds are in bits and file sizes in bytes, as explained in our guide to bytes versus bits.
Keeping Your Own Files Small
Large images slow down web pages. Resize and compress them with our Image Compressor and Image Resizer before uploading.
Seeing Bytes Add Up Yourself
The easiest way to feel the scale is to start from the smallest unit. Our binary translator converts text into its byte-by-byte binary form, so typing even a short sentence shows exactly how many bytes it takes up — a useful reference point before jumping to thinking in thousands, millions, or billions of them. To understand what separates a byte from the bit it’s built from, see our guide on byte vs bit.