The sizeof operator returns the number of bytes occupied by a variable of a given type. The type specified as an operand to sizeof must be an unmanaged-type (25.2). sizeof-expression : sizeof(unmanaged-type) The result of the sizeof operator is a value of type int. For certain predefined types, the sizeof operator yields a constant value as shown in the table below. Expression Result sizeof(sbyte) 1 sizeof(byte) 1 sizeof(short) 2 sizeof(ushort) 2 sizeof(int) 4 sizeof(uint) 4 sizeof(long) 8 sizeof(ulong) 8 sizeof(char) 2 sizeof(float) 4 sizeof(double) 8 sizeof(bool) 1 For all other types, the result of the sizeof operator is implementation-defined and is classified as a value, not a constant. The order in which members are packed into a struct is unspecified. For alignment purposes, there may be unnamed padding at the beginning of a struct, within a struct, and at the end of the struct. The contents of the bits used as padding are indeterminate. When applied to an operand that has struct type, the result is the total number of bytes in a variable of that type, including any padding.