How to calculate the number of years in a kalpa?

Wikipedia's Kalpa(aeon) in Buddhism article says, > In another simple explanation, there are four different lengths of kalpas. A regular kalpa is approximately 16 million years long (16,798,000 years<a href="/redirect?url=http%3A%2F%2Fen.wikipedia.org%2Fwiki%2FKalpa_%2528aeon%2529%23Buddhism" class="external-link" target="_blank" rel="nofollow noopener">[1] <i class="fas fa-external-link-alt fa-xs"></i></a>), and a small kalpa is 1000 regular kalpas, or about 16 billion years. Further, a medium kalpa is roughly 320 billion years, the equivalent of 20 small kalpas. A great kalpa is 4 medium kalpas, or around 1.28 trillion years. I just went through the Visuddhimagga, and could not find where or how that time in years is calculated. I was wondering how to calculate it. Please explain how it's calculated, with reference to scripture where Lord Buddha mentioned it, and/or where the calculation or the result of the calculation is described, perhaps in the Thripitaka or Visuddhimagga? --- <a href="/redirect?url=http%3A%2F%2Fen.wikipedia.org%2Fwiki%2FKalpa_%2528aeon%2529%23Buddhism" class="external-link" target="_blank" rel="nofollow noopener">[1] <i class="fas fa-external-link-alt fa-xs"></i></a> Wikipedia's reference is to a book: > Epstein, Ronald B.(2002). Buddhist Text Translation Society's Buddhism A to Z p. 204. Buddhist Text Translation Society. ISBN 0-88139-353-3, ISBN 978-0-88139-353-8. Perhaps that book may have a reference to where they found it, but I still haven't find that book.