The optimal biogas system design model (OBSDM) described in this paper is intended to be used as a decision-making tool to increase awareness of the potential of biogas technology for different applications in Sub-Saharan Africa (SSA). The decision-making tool identifies the most suitable biodigester design based on user defined inputs, including energy and fertiliser requirements; feedstock (type, amount, and rate of supply); water supply; land use (area, soil type, ground water level); climate (temperature and rainfall); construction materials available locally; and the priorities (based on sustainability criteria) of the intended biogas user. The output of the model provides a recommended design with estimates of the expected costs, energy and fertiliser production, and links to contact biodigester suppliers. In order to test the model, data from household surveys conducted in rural regions of Kenya and Cameroon were used as inputs to the model. An innovative fixed dome biodigester design, which uses stabilised soil blocks instead of bricks, was identified as optimal for both Kenyan and Cameroonian rural households. The expected performance of the optimal biogas system design from the model output was consistent with survey data on existing biogas systems in the region. (C) 2017 Elsevier Ltd. All rights reserved.