Just popped open Task Manager...
calculator.exe is at 74 MB working set, 24 MB Memory (private set), 50 MB Memory (shared working set), 48 MB commit size.
mIRC.exe is at 31 MB working set, 13 MB Memory (private set), 18 MB Memory (shared working set), 38 MB commit size.
Doesn't matter which value you use for "How much memory does this program use?". mIRC is smaller in all of them.