This paper presents models developed to predict friction head losses in drip irrigation laterals. Some domestic and imported drip irrigation laterals equipped with integrated in-line and on-line emitters placed at different spacings ranging from 0.2 and 1 m were considered in this study. The parameters affecting the variation in friction head losses in laterals were defined as dimensionless terms using Buckingham's Pi theorem. Two mathematical models were developed in this study. In order to develop a model for integrated in-line emitters, experimental friction head losses data from 16 different drip irrigation pipes with above-mentioned spacings were used and the model developed accounted for 98.53% of the variation in the data. Another model developed was for predicting the friction head losses in laterals with on-line emitters. For the development of a model, experimental friction head losses data from six different drip irrigation pipes equipped with on-line emitters with above-mentioned spacings were used. The model developed for on-line emitters was able to explain the 98.76% of the variation in the data collected in the laboratory.