how create length of a data or data block

(1)
data1 DB "T&D Research MEMORY.COM"
data1_length EQU $-data1 ; //upper string length

(2)
GDT_TABLE GDT <0,0,0,93h,0>
.............
.............
GDT_LEN = $ - OFFSET GDT_TABLE ;length of GDT