A conventional railway system usually has multiple train types with various service patterns operating on the same line. Differences in train characteristics lead to varied capacity effects on the system. “Rail line capacity” is commonly defined as the maximum number of trains that can be operated on a section of track with an expected level of service within a given time period. However, a particular unit (trains/hour or trains/ day) does not reflect the train type the unit refers to. In this study, a new concept is proposed, namely, the base train equivalent (BTE), along with a standardization process to classify different train types in accordance with the particular type defined by the user. This concept is similar to the passenger car equivalent, which converts trucks to passenger car units in classifying highway transportation. A delay-based approach is also developed to determine BTEs on the basis of results obtained from two common capacity evaluation methods: parametric capacity analysis and simulation. With the proposed method, capacity measurements from different lines or systems can be compared and evaluated, resulting in meaningful and useful attributes.