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[1]), 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?



[1] 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.
As far as I know, the words used in Buddhist Kalpa in a lot of cases, 

for example: Existence, life reduced (when life human destiny decreased from 84,000 years to 10 years),increased lifetime (as opposed to lifetime reduction),

Sub-Kalpa (approximately 16 million years),

Mid-Kalpa (20 sub-life),

Big-Kalpa (4 centered life = 1.3 billion years),

and countless Kalpa ..etc