A megabyte is a unit for measuring how much computer information something is — roughly a million bytes. It is written MB. A byte is eight bits, and one byte holds about one letter of plain text, so a megabyte is around a million letters: a long book in plain text, one decent photo, about a minute of music. It is the unit people reach for when talking about the size of files, photos, apps, and mobile data allowances. Here is the messy part, and your students will meet it. Strictly, in the way computers count, a megabyte is 1,024 kilobytes (1,048,576 bytes), because computers count in twos, not tens. But hard-drive and phone companies often use the round one million instead, because it makes their number look bigger. Both uses are out there, which is why a '500 GB' drive shows up on your computer as something less. Some people write MiB (mebibyte) for the strict 1,024 version to keep the two apart, but almost nobody says that out loud. In everyday speech the megabyte now feels small — phones and files moved on to gigabytes long ago — so you meet it mostly for photos, documents, and email limits.

百萬位元組、兆位元組（台灣口語幾乎都直接講英文字母「MB」，或說「幾 M」，例如「這張照片三 M」）