c# get excel column number from letter
public static int ColumnNameToIndex(string name)
{
var upperCaseName = name.ToUpper();
var number = 0;
var pow = 1;
for (var i = upperCaseName.Length - 1; i >= 0; i--)
{
number += (upperCaseName[i] - 'A' + 1) * pow;
pow *= 26;
}
return number;
}