Here are some examples:
* The damage caused by the hurricane was incalculable. (The destruction was so widespread and severe that it was impossible to quantify.)
* The benefits of a good education are incalculable. (The positive impact of education is so extensive and long-lasting that it cannot be measured.)
* The potential impact of this new technology is incalculable. (We don't know for sure how this technology will change things, so we can't predict its effects.)
In essence, "incalculable" signifies something beyond our ability to measure or understand fully.