Opportunities for farmers to participate in greenhouse gas (GHG) credit markets require that growers, students, extension educators, offset aggregators, and other stakeholders understand the impact of agricultural practices on GHG emissions. The Farming Systems Greenhouse Gas Emissions Calculator, a web-based tool linked to the SOCRATES soil carbon process model, provides a simple introduction to the concepts and magnitudes of gas emissions associated with crop management. Users choose a county of interest on an introductory screen and are taken to the input/output window, where they choose crops, yields, tillage practices, or nitrogen fertilizer rates. Default values are provided based on convention and county averages. Outputs include major contributors of greenhouse gases in field crops: soil carbon change, nitrous oxide (N[subscript 2]O) emission, fuel use, and fertilizer. We contrast conventional tillage and no-till in a corn-soybean-wheat ("Zea mays" L.-"Glycine max" (L.) Merr.-"Triticum aestivum" L.) rotation and compare continuous corn fertilized at 101 and 134 kg N ha[superscript -1]yr[superscript -1]. In corn years, N[subscript 2]O was the dominant GHG, due to high fertilizer requirements for corn. No-till management reduced greenhouse gas emissions by 50% due to net soil carbon storage. Continuous corn fertilized at 101 kg N ha[superscript -1]yr[superscript -1] emitted 1.25 Mg CO[subscript 2] equivalents ha[superscript -1]yr[superscript -1] compared with 1.42 Mg CO[subscript 2] equivalents ha[superscript -1]yr[superscript -1] at 134 kg N ha[superscript -1]yr[superscript -1], providing a 12% GHG savings. The calculator demonstrates how cropping systems and management choices affect greenhouse gas emissions in field crops. (Contains 4 tables and 4 figures.)