The minimum size for a User Defined Type (or really any data type) is 32 bits. If you keep adding more BOOL tags you will see that size stay constant until you reach 33 BOOLS, and then it would jump to 8 bytes.
Keep in mind that how you organize them makes a difference too. For example if I had:
BOOL (bit 0 in byte 1)
BOOL (bit 1 in byte 1)
BOOL (bit 2 in byte 1)
DINT (bits 0 - 31 in byte 2
BOOL (bit 0 in byte 3)
BOOL (bit 1 in byte 3)
DINT (bits 0 - 31 in byte 4)
That would require 16 bytes. But if we rearranged it to:
BOOL (bit 0 in byte 1)
BOOL (bit 1 in byte 1)
BOOL (bit 2 in byte 1)
BOOL (bit 3 in byte 1)
BOOL (bit 4 in byte 1)
DINT (bits 0 - 31 in byte 2
DINT (bits 0 - 31 in byte 3
That would require 12 bytes,
OG