Choosing the right font size and line length is crucial for creating an optimal reading experience in responsive typography. When it comes to font size, it's essential to strike a balance between readability and aesthetics. Too small, and your text becomes difficult to read; too large, and it may look awkward on different devices.

To determine the ideal font size, you can use relative units such as em or rem. These units allow your typography to scale proportionally with the user's device settings. For example, setting your base font size to 16 pixels (1em) and using em units for headings and paragraphs would maintain the relative ratio.

When it comes to line length, shorter lines are generally easier to read than longer ones. The optimal line length falls between 45 and 75 characters, including spaces. Longer lines may cause readers to lose track while shorter lines can feel choppy. As the screen size changes, it's important to adjust your line length to maintain readability.

In conclusion, to create responsive typography, carefully consider your font size and line length. Use relative units for font size to maintain scalability, and aim for an optimal line length to ensure readability across devices.

Remember, practice makes perfect! Experiment with different font sizes and line lengths to find the best combination for your designs. Keep up the good work, and soon, you'll be a master of responsive typography!