How do I check my screen DPI?

How would one go about determining the DPI, or dots per inch, of their screen? Is there a specific setting or menu that I should be looking for within my operating system? Are there any third-party tools or applications that can assist in this process? Additionally, what factors might affect the DPI of my screen, and how can I adjust them if necessary? It's important to me to ensure that my screen is displaying content at the optimal resolution, so any guidance on this matter would be greatly appreciated.