Responsive web design is based on screen resolution or screen size?

Question

For mobile devices the resolution is actually big, only screen size is small. Based on that: - For **websites design**, do we target screen resolution (e.g 1920x1080)? - And for **mobile apps**, do we target the screen size?

Answer 1

when you're dealing with responsive design, you specify percentages, not the number of pixels, i.e. if you have to have a tabular structure with 4 columns of the same width, you would specify width of each column as 25%