The 'Units' metric shows the total number of products purchased within all orders. This metric is vital for eCommerce sites in measuring conversion. You can combine this metric with any dimension to see what which dimension values contributed to how many products were purchased. For example, you could see the top campaigns (using the Tracking code dimension) or top internal search terms (using an eVar ) that contributed to products purchased.
Compare orders and units
The Orders metric only records the number of purchase events. The 'Units' metric is typically higher than 'Orders' because customers can purchase more than one product. In these cases, a single order exists with multiple units.
If you have orders higher than units, Adobe recommends to check the integrity of your implementation. It is likely that your products variable is not set correctly on purchases, which is typically undesired behavior.