The paper presents a novel, theoretically sound approach to the analysis of defence policy and force models and first results of its implementation. The approach is based on comparison of defence policies and cost data under the hypothesis that a particular defence policy relates to a specific set of defence capabilities with the respective impact on cost. We identified six factors, or dimensions, of defence policy with major impact on the cost of the respective capabilities, and used publicly available data to construct a model of capability cost, expressed in defence budget per active duty military personnel in constant purchasing power parity dollars, as a function of the six factors. Then the model was used to define what might be the reasonable force size of the Bulgarian Armed Forces in 2015 under three plausible alternative defence policies. The final section of the paper outlines strengths and limitations of the approach, as well as outputs and potential outcomes from its implementation.