This example maps one declared small-screen body size to one declared large-screen size. It demonstrates the calculator contract, not a universal reading-size rule. Real font metrics, line length, language, zoom and user needs still decide whether the resulting typography works.
Enter the four endpoints and a 16px root
Use 320 for the small viewport, 1200 for the large viewport, 16 for the small value and 20 for the large value. Keep rem + vw output, a 16px root and six decimal places. The exact slope is 4/880, or 1/220 px per viewport px, and the exact intercept is 160/11px.
Copy the generated font-size
The generated value is clamp(1rem, 0.909091rem + 0.454545vw, 1.25rem). At widths below 320px, the lower bound wins; between 320px and 1200px, the rounded preferred expression grows linearly; above 1200px, the upper bound wins. The endpoint evidence shows the small numerical differences created by six-decimal serialization.
Review reading behavior in the real component
Apply the declaration to the actual body text, then test long and short content, every supported language, browser zoom and narrow intermediate widths. Confirm line height and measure separately. Passing through the requested numerical endpoints does not prove that either endpoint was a good choice or that the component meets accessibility requirements.