This paper analyzes the correlations between the problem domain measures such as the number of distinct nouns and distinct verbs in the requirements artifacts and the solution domain measures such as the number of software classes and methods in the corresponding object-oriented software. For this purpose, 14 completed software development projects of a CMMI Level-3 certified defense industry company have been analyzed. The observed strong correlation is taken as the indication of linear relationship between the measures and a size estimation model based on linear regression analysis is proposed. Prediction performance of the method is analyzed on the 14 software projects. Moreover, it has been observed that there is a high correlation between the problem domain measures and the development effort. Therefore, the linear regression analysis is also used to estimate the effort in terms of the problem domain measures. The effort estimations are also evaluated and compared with the efforts predicted using the size measured by the COSMIC Function Point (CFP) method. The results show that the proposed method provides more accurate effort estimates compared to the effort estimated by using CFP size measurement.