Developer Builds Offline BMI Calculator Using Pure HTML With No APIs or Frameworks

A developer shared lessons from building a fully offline, single-file BMI calculator without any third-party dependencies or server calls, aiming to avoid bloated bundles and privacy concerns. The core technical challenge was not the BMI formula itself but handling unit conversions across metric, imperial pounds, and UK stone systems, with all values converted to metric internally before display. The project also addressed UX issues such as non-linear BMI category visualization, input validation with generous but sensible limits, and jitter-free number display using monospace fonts. Dark mode was implemented purely through CSS custom properties, while responsive design ensured usability down to 320px screen widths. Internationalization required separating label translation from number formatting logic to correctly handle cultural differences in how measurements are expressed.