C++ FAQ Celebrating Twenty-One Years of the C++ FAQ!!!
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Section 26:
[26.2] What are the units of sizeof?

Bytes.

For example, if sizeof(Fred) is 8, the distance between two Fred objects in an array of Freds will be exactly 8 bytes.

As another example, this means sizeof(char) is one byte. That's right: one byte. One, one, one, exactly one byte, always one byte. Never two bytes. No exceptions.