<p>Nielsen’s heuristics have served as a guideline for designing user interfaces and evaluating their usability for more than thirty years. Heuristic evaluation relies largely on qualitative analysis and there has been limited use of quantitative metrics in it so far. In this paper, we propose a new approach for heuristic evaluation based on Nielsen’s heuristics with an emphasis on quantitative metrics for assessing the usability of user interfaces. The approach is straightforward and suitable for use in the software industry. We used the approach to perform heuristic evaluation of four software products and five experts could identify 53 usability problems in the software products on an average. A quantitative analysis revealed that concurrence percentage, a measure of the extent of overlap among the usability problems identified by the different evaluators, was between 21 and 44% for the software products. Normalized severity entropy of the software products varied from 0.82 to 0.94, and these high values denoted that the catastrophic and major usability problems identified by the evaluators violated many of Nielsen’s heuristics. Usability index, an estimate of the usability of the user interface as a whole, varied between 51.63 and 60.96 for the software products. We believe that such quantitative metrics can help in drawing useful inferences based on heuristic evaluation and comparing the results for different software products, and have proposed norms for them.</p>