Richard, I assume that it is the minimum count of numbers that you are after.
Why not sort by those numbers (descending) and then divide a cumulative sum
function as you progress down the row, by the total sum and have it report a
row count column when it is equal to or greater than 80%.

With the above method you could put the formula in one column if necessary
when it is sorted. Two columns would be clearer. To come up with a single
formula in one cell on unsorted data requires an expert on array formulas,
I'm not sure whether it can be done this way.

"Richard" wrote:

I have a column of numbers and would like to know how many of those numbers
make up 80% of the total of the column. Does anybody have a formula for that?