With Texel Density Checker you can: 

• Calculate Texel Density for mesh for different texture size (includes non-squared textures and custom size)
• Rescale UV for getting of target Texel Density
• Copy Texel Density from one object to others
• Select faces for same Density/UV Space
• Visualize Texel Density/UV/Islands with Checker material and vertex color

It is Addon with GNU GPL License. You can download source code from GitHub or install directly from Blender Extensions

Texel Density Checker simple for use. You need select your mesh (or faces) and texture size and just click button.

• Added presets for small texture sizes (PR from @whodgson)
• Custom checker image assignment

• 2D cursor position changing after setting texel density when Pixel Coordinates are enabled.
• Startup errors caused by running context-dependent operators without an active UI area.

See full CHANGELOG