sizeof()

returns an integer of the memory size of the given variable or datatype enum.

Example

sizeof(bool) // will be one

This is the byte-size

int x{};
sizeof(x) // 4 bytes

Size Compendium

For unsigned:

char  : 1 byte
short : 2 bytes
int   : 4 bytes
long  : 4 bytes
float : 4 bytes
double: 8 bytes

If its signed, then its going to be double the size.