Abstract—With proliferation of internet and web-applications usage, server performance is a critical research area in last decade. This paper presents a nonintrusive approach to estimate server response time for user-initiated web-page requests from web-server access-log data using a variant of fuzzy c-means algorithm. The approach presented here is particularly suitable for a system of web-application(s) accessed concurrently by multiple users and running in a constrained production environment where minimal amount of monitoring or logging data is available. In such scenarios, proposed approach will be useful conducting advance system level testing as well as in verifying compliance to service level agreements (SLAs). Algorithm presented here has been tested using open source web application JPetStoreApp and java based load testing framework Grinder.