UNIT SWAP
A quick unit converter for everyday length, weight, volume, speed and temperature conversions.
Two identical dropdowns can hide very different maths. Most units convert by multiplying, but temperature needs an offset, and a gallon means something different in the US and the UK.
Every unit converts through its category's base unit. Length, weight, volume and speed use simple factors, and temperature uses its own offset-aware rules. US and UK units are labelled separately, so the interpretation is always visible.
It covers 31 units across five categories. Results show sensible decimals for their size and switch to scientific notation for very large or very small values.
The limit: it will convert a temperature below absolute zero without complaint, there are no tests, and it has no area category or Nepali units, which are the conversions people in Nepal most often need.
Next I would add land units such as ropani, aana, bigha and kattha, gold in tola, input checks for impossible values, and tests.