The foundation STUNS is investigating a possible move of the Origo office with tenants to a new office space. The Origo office today has a low utilization rate which makes it interesting to investigate the possibility of having an office space based on the ratio of occupancy. The purpose of this study is to calculate a ratio of occupancy with the corresponding risk of overcrowding and estimate the energy reduction. When adapting the new office space to the optimal ratio of occupancy, three office design proposals will be created. With the chosen optimal ratio of occupancy at 68 percent, the risk of overcrowding spanned between 0.3 to 0.6 percent. All proposals based on the optimal ratio of occupancy lead to electricity and cost reductions. An open office design leads to an electricity reduction of 686 kWh and a cost reduction of 168 kSEK per month. An activity based workplace leads to an electricity reduction of 540 kWh and a cost reduction of 132 kSEK per month. An individual office design leads to an electricity reduction of 452 kWh and a cost reduction of 111 kSEK per month. A sensitivity analysis is made by altering input parameters. The analyzed parameters are the unique attending employees, the transition probabilities and the choice of risk of overcrowding. For optimal utilization an open office space is the best alternative because it requires least square meters based on the same ratio of occupancy and workspaces. But when considering more aspects about work habits, employees’ opinions and behaviour the optimal office design may need a different structure.