As described in ArcGIS Online: Understand credits, storage in ArcGIS Online costs credits. As of July 2019, the cost of feature storage, excluding feature attachments and feature collections, is 2.4 credits per 10 MB stored per month calculated hourly. The following formula applies to calculate the cost of credits per item, per month:
(Size in MB / 10) * 2.4 credits = number of credits for feature storage per month
For example, a hosted feature layer named UK_election_2015 is 256 MB in size. Therefore, applying the formula:
(256 / 10) * 2.4 credits = 61.44 credits per month for storage
Sometimes users may want to see a list of the organization's hosted feature layers consuming these storage credits, including viewing the size of that data. The following instructions describe how to do so.