A simple, practical analytical approach to capacity planning is described in the context of semiconductor wafer fabrication (fab) areas and implementation of Drum-Buffer-Rope methodology. The well validated model integrates bottleneck identification with predictors of headcount requirement, fab activity levels, cycle time and inventory curves, financial impacts and other metrics, as desired, for given volume and mix. The model, used in combination with the knowledge of local experts, provides information for medium or long range planning and for focusing improvement efforts for maximum effect. Opportunities for improvement are simply explained, verified, quantified and prioritized through the use of specific tool models and of Overall Equipment Effectiveness (OEE) as a measure of equipment performance. Several manufacturing areas on the same site can be simultaneously modeled, showing the effect of a change on the entire site.