With Texel Density Checker you can:
Calculate Texel Density for model for different texture size (includes non-squared textures and custom size)
Rescale UV for getting texel density what you want
Copy Texel Density from one object to others
Select faces for same Density
Texel Density Checker is simple for use. You need to select your mesh (or faces) and texture size and just click the button.