Software effort and cost estimation is a very important activity that includes very uncertain elements. In the context of object oriented software, traditional methods and metrics were extended to help managers in this activity. The metric Use Case Points (UCP) is an example of metric that can be used. UCP considers functional aspects of the Use Case (UC) Model, widely used in most organizations in the early phases of the development. However, the metric UCP presents some limitations mainly related to the granularity of the UC. To overcome these limitations, this paper introduces two metrics, also based on UCs. The first one, named USP (Use Case Size Points), considers the internal structures of the UC and better captures its functionality. The second one, named FUSP (Fuzzy Use Case Size Points), considers concepts of the Fuzzy Set Theory to create gradual classifications that better deal with uncertainty. Results from an empirical evaluation show the applicability and some advantages of the proposed metrics.