The stochastic nature of extreme ultraviolet (EUV) resist exposure leads to variations in the resulting acid concentration, which leads to line-edge roughness (LER) of the resulting features. Using a stochastic resist simulator, we predicted the mean and standard deviation of the acid concentration for an open-frame exposure and fit the results to analytical expressions. The EUV resist exposure mechanism of the PROLTIH Stochastic Resist Simulator is first order, and an analytical expression for the exposure rate constant C allows prediction of the mean acid concentration of an open-frame exposure to about 1% accuracy over a wide range of parameter values. A second analytical expression for the standard deviation of the acid concentration also matched the output of the simulator to within about 1%. Given the assumptions of the PROLTIH Stochastic Resist Simulator, it is possible to use the results of this paper to predict the stochastic uncertainty in acid concentration for EUV resists, thus allowing optimization of resist processing and formulations and contributing to a comprehensive LER model.