View the calculator at

This calculator allows you to input arbitrary ratios (like for a cooking recipe, a home improvement project, whatever) and then scale the recipe up and down.

It’s helpful because you can change any resulting value. For example, suppose you have a cake recipe that needs 4 cups of flour, but you only have 3.5 cups of flour. This will scale all the other ingredients accordingly.

It’s a single-page application built with React and basic HTML elements. The deployment is literally just serving up a static HTML and JS file with modern-ish JS syntax (may the odds be ever in your favor, IE 10 users). It uses React hooks because that’s how I like expressing the logic. If this paradigm interests you, you may be interested in commit 3e3fe18 as a barebones template.