Anaerobic co-digestion (AcoD) of dairy manure and a wide variety of off-farm feedstocks including pre- and post-consumer food wastes can improve economic feasibility of on-farm anaerobic digestion (AD). Added feedstocks can result in substantial digester effluent volume increases that must be properly managed and depend on the feedstock’s characteristics. Digester influent and effluent flow meters are the best primary measurement method for quantifying flows and supporting tipping fees; however, they are often not standard equipment on most farm systems. Absent adequate metering, acceptable influent-effluent digester volume reduction calculations can provide the basis for assessing additional material handling compensation, especially when systems involve third-party AD operators or off-farm owner-operators. When on-farm AcoD systems involving third-party partnerships are in place, it is important to determine the effect AcoD has on influent-effluent volume differences. This two-part fact sheet set summarizes a recommended method to calculate influent-effluent volume differences based on published work and provides an array of results applying this method on representative on-farm AcoD scenarios.