Multimodal freight vehicle assignment models require numbers of vehicles to generate origin-destination matrices. Most current freight flow data are provided as total volume or value. Presented are the development and results of conversion models for converting weight to number of rail cars as one component of a multimodal planning activity. The 1992 rail waybill sample was used for developing the conversions. Only loaded cars were used for conversions. Therefore, empty cars are not included in the models. Evaluation of these conversions was performed by using 1993 Commodity Flow Survey data. On the basis of the evaluation, recommendations on conversion models are made.