Abstract: Disclosed herein is a computer implemented method and system for evaluating a mathematical expression spoken in a natural language by a user. The disclosed method and system provides a natural language speech recognition calculator comprising a speech recognition engine. The spoken mathematical expression is transmitted to the speech recognition engine via an audio input device. Mathematical entities of the spoken mathematical expression are extracted and represented in a hierarchical recursive format of a speech recognition grammar implemented by the speech recognition engine. A symbolic mathematical expression is generated from the extracted mathematical entities and then normalized with common measurement units. The normalized mathematical expression is then evaluated to generate a mathematical result. The mathematical result may be synthesized by a text-to-speech engine to produce a voice output.