In a recent message to Wieland Willker's textual criticism list (here), Daniel Wallace estimates the number of pages of extant Greek NT manuscript at 2.5 million.
In a Kenneth W. Clark memorial lecture of 1997, Bart Ehrman (here) says:
'No one knows for sure how many differences there are among our surviving witnesses, simply because no one has yet been able to count them all. The best estimates put the number at around 300,000, but perhaps it's better to put this figure in comparative terms. There are more differences among our manuscripts than there are words in the NT.'
What is the basis of Ehrman's calculation? There is no further reference.
If Wallace's and Ehrman's estimations are both correct then it strikes me that the overall rate of unique variants per manuscript page is incredibly low. This is only just above one unique variant per 10 'pages' (which I presume in Wallace's original context, i.e. of photography, means either a single side or the facing sides of an open codex). Obviously the rate of unique variants per page is not the same as the rate of errors since the same error could occur independently in two manuscripts and then only count as one unique variant. Nevertheless, I still find the ratio rather low. Has Ehrman been too conservative?