Our shipping calculator analyzes each shipment to determine the path it takes, how much it weighs, and the mode of transportation that is used in transport. Shipping carriers such as FedEx, UPS, DHL, and USPS provide information on the transfer locations for the package as it completes its journey. Using the carrier information, our calculator analyzes the time that it takes for the package to get from point to point. For legs that are determined to be by truck, we calculate the best travel route for that leg to determine the actual distance traveled. For air transport legs, we calculate distance "as the crow flies".

Professor Arpad Horvath at UC Berkley has published a study that provides the greenhouse gas generated per ton-mile for each mode of transportation. We use that data to calculate the CO2 generated by the shipment.

To achieve the highest level of accuracy, our calculator waits to finish the calculation until after the shipment is completed, when the full details of the shipment are available.