HRCalc is an astronomical calculator used to derive properties of stars given a star's luminosity and surface temperature. With these values, HRCalc can derive the radius of a star and display stellar size relationships using graphical models.

HRCalc allows you to experiment with various luminosity and temperature settings to determine the effects of these parameters on a star's theoretical size. Additionally, this tool allows you to plot stars on a Hertzsprung-Russell (H-R) Diagram, which is an important tool used in Astronomical Sciences to compare different types of stars. Plots generated with HR Calc can be saved as XML files and reloaded at a later time. HRCalc comes with a database containing thousands of stars which can be modeled in the interface and plotted.

This tool is designed for astronomy educators, students and enthusiasts to help them understand the relationship between stellar temperatures, luminosities and sizes, and where these stars fall on the H-R Diagram. It is also useful in the classroom, allowing instructors to integrate this tool into their astronomy courses as a hands-on learning or demonstration tool.