Determine total size disk(DVD or CD)

How to determine total size disk(DVD or CD)?

I am use NeroCom

There is a TotalCapacity property on NeroCDInfo object. This gives you the capacity in blocks.

TotalCapacity - is not documented(Nero SDK -1.04)
And TotalCapacity property dont contained in NeroCDInfo object
(C++ Builder 6 and Nero- 6.3.1.15)