The average ranking is calculated as follows, where:
w = weight of ranked position x = response count for answer choice
(x1w1 + x2w2 + x3w3 ... xnwn)/ Total response count
Weights are applied in reverse. In other words, the respondent's most preferred choice (which they rank as #1) has the largest weight (7), and their least preferred choice (which they rank in as #7) has a weight of 1. We add together all of the respondents weighted ranks, and then divide by the total number of respondents.
We apply weights in this way to ensure that when the data is presented on a chart, it's clear which answer choice is most preferred.