Days Sales Outstanding (DSO) is a standard accounting metric, defined as a measure of the average number of days that a company takes to collect revenue after a sale has been made. A low DSO value means that it takes a company fewer days to collect its accounts receivable. The formula to calculate DSO is written as: accounts receivable * (total sales/number of days).
This is caculated based on Accounts Receivable and Net Sales figures reported by Amazon.
Last reported quarter 2017 Q3 it was 22.02, up by 20% from 18.31 the same quarter a year before.
Source: Amazon Quarterly Results.