/Zp8

In words, integral types and pointers up to eight bytes in size are stored at their natural alignment. Larger types are stored at eight-byte alignment.

TypeAlignment
BYTE, char, UCHAR 1-byte alignment
WORD, WCHAR, short, USHORT 2-byte alignment
DWORD, int, long, UINT, ULONG, float, 32-bit pointer 4-byte alignment
QWORD, __int64, unsigned __int64, double, 64-bit pointer 8-byte alignment

In other words (saying it a third time), let T be an integral or pointer type. If sizeof(T) ≤ 8, then T is aligned at a sizeof(T)-byte boundary. If sizeof(T) ≥ 8, then T is aligned at an 8-byte boundary.