Explanation
SUMPRODUCT accepts the range B3:B6 as an array of four cells.
For each cell in the array, LEN calculates the length of the text as a number.
The result is an array that contains 4 numbers.
SUMPRODUCT then sums the items in this array and returns the total.
LEN will also count characters in numbers, but number formatting is not included.
SUMPRODUCT Function
The Excel SUMPRODUCT function multipliesrangesorarraystogether and returns the sum of products.