High energy electrons on interaction with residual gas molecules present in the vacuum chamber of electron storage rings produce gas bremsstrahlung radiation. Extensive studies have been carried out in past to evaluate dose rate from gas bremsstrahlung using various simulation techniques with air as target gas. From these studies, empirical relations were deduced to evaluate gas bremsstrahlung dose rate. However storage rings at ultra high vacuum level contains primarily hydrogen and hydrocarbon gases as residue. In this work, effect of residual gas composition in vacuum chamber on gas bremsstrahlung dose rate in electron storage rings of energy range 1–3 GeV has been studied using FLUKA Monte Carlo code. Simulation study was performed to investigate effects on energy distribution, angular distribution and absorbed dose rate of gas bremsstrahlung due to various composition of residual gas normally encountered in vacuum chambers of storage rings. The gas bremsstrahlung dose rate was found to depend on effective atomic number and molecular mass of the residual gas molecules. From the study, a new empirical formula for the estimation of gas bremsstrahlung dose rate is proposed.