Biopharmaceuticals (or biologics), large molecule therapeutics typically produced using biotechnology, are a rapidly growing segment of the pharmaceutical market. As such, the environmental footprint of the production of these molecules is coming under scrutiny from various stakeholders such as healthcare providers, investors, and even employees. Process mass intensity (PMI), originally adopted for small molecules by the Green Chemistry Institute Pharmaceutical Roundtable, is a simple metric that can also be applied to evaluate the process efficiency of biopharmaceutical production. PMI for biologics is defined as the total mass input in kg of water, raw materials and consumables, required to make 1 kg of active pharmaceutical ingredient. Six large pharmaceutical companies participated in a benchmarking exercise to calculate the PMI for monoclonal antibody (mAb) production. On average, 7700 kg of input is required to produce 1 kg of mAb. Over 90% of the mass is due to water use, highlighting the water-intensive nature of biologics production.