[divbzero]

DuckDuckGo does do unit conversions “100 JPY in EUR” [1] and unit-less calculations “2^32 - 1” [2].

[1]: https://duckduckgo.com/?q=100+JPY+in+EUR

[2]: https://duckduckgo.com/?q=2%5E32-1

But like you I drop back for unit-aware calculations. For those an alternative to Google is Wolfram Alpha “!wa speed of light / 400nm in terahertz” [3] which also allows for symbolic computation “!wa integral of 2x” [4].

[3]: https://duckduckgo.com/?q=!wa+speed+of+light+%2F+400nm+in+te...

[4]: https://duckduckgo.com/?q=!wa+integral+of+2x

[dontbenebby]

When DDG fails for a conversion I usually append !wa and Wolfram Alpha parses it easily