To qualify for Amazon Compact by Design, products must have best-in-class “unit efficiency.”  Amazon says it uses product attributes such as item package dimensions, item weight, and the number of units to calculate the unit efficiency of a product. 
 
Unit is defined as the total amount of product in the container Amazon is evaluating. 
 
This is standardized across a product category, such as fluid ounces in cleaners, loads in laundry detergent, and ounces in coffee.

Unit efficiency is calculated as (cubed volume per unit) x (weight per unit). This metric allows Amazon to calculate the volume and weight utilization for the number of units a product delivers. In this equation, a lower unit efficiency value means a more efficient design. 
 

As an example, Amazon highlights a concentrated laundry detergent that can deliver the same number of units (loads) in a smaller volume and weight than a non-concentrated detergent.
 
To set thresholds, Amazon calculated unit efficiency across items in a product category, and set thresholds to recognize the most efficient products within each product category. Products with a unit efficiency better than the category threshold qualify for Compact by Design, and get to be a part of Climate Pledge Friendly.
 
Here are the category thresholds.