Days inventory on hand, also known as a days of supply, along with inventory turns, is a measure of inventory investment. While turns may be one of the most basic measures of an organization’s “leanness,” days inventory on hand perhaps helps lean practitioners better visualize the magnitude of (excess) inventory and its impact on a value stream’s lead time. This is especially applicable when the notion of inventory extends beyond parts and finished goods to transactional (i.e., files, contracts, etc.) and healthcare (i.e., tests, reports, etc.) value streams.