Convert between diferent Density of pixel in Android

Greeting !!
I wonder how can I measure the diference between diferent screen resolution in Android, so well let me explain with a simple example, I render a texture into a Android phone with a fixed size (SDL_Rect )and everything went ok but when I tried to render the same texture in another phone the image went wrong, could somebody tell me how can I understand this it, thank you in advance. cheers