No need count letterboxes.
You want to know this particular block has total how many units,
just go facing the block and count from left to right (right to
left also can) how many units on a storey (example 16 units on
storey 2) multiply by no. of storeys excluding void deck (example
11 storeys flat) and you get total 160 units.
crap you beat me to it =(