The superstructure weight of bridges and viaducts influences the behavior of bridges and viaducts during earthquakes, but in order to grasp it, a detailed load calculation is usually required. In this paper, we developed a simple method for estimating superstructure weight of railway bridges and viaducts. Specifically, the girder weight per unit length according to the type of girder, the weight of the track according to the type of track were arranged from existing literature, and an simple estimation formula for superstructure weight was created. Regarding the girders for which the superstructure weight is calculated in detail, the results of the estimation formula and the detailed calculation were compared, and it was confirmed that the superstructure weight can be estimated with a maximum error of about 10%. This result is expected to be applied to the efficient construction of seismic response analysis models for a huge number of railway bridges and viaducts.