Note: Type words 'wa' and 'o' as 'ha' and 'wo', because that's how they are written in japanese.
Romaji:
Word separator:
Encoding:

If your text is ENGLISH, try english to romaji converter.
If your text is otherwise NOT standard romaji (but Finnish for example), use older converter instead.
Those two also offer katakana.
If you want kanji! Use the dictionary instead.

Written by Bisqwit (https://iki.fi/bisqwit/)

Syllable list is also available. It lists all the katakana/hiragana syllables.
It is available sorted another way too. A shorter list is there too. Some other versions also...

Disclaimer: The accuracy of the operation of this converter is strictly limited to the progress of my Japanese studies.

Errors, if you find, report to me via email.

Source code is available (php). It might interest you, as it is short (~340 lines (well, once was)), but contains hiragana encoding in iso-2022-jp, euc-jp, shift_jis and unihtml (without external programs), plus a quite elegant parsed table for romaji to hiragana conversion. It could be easily extended to support different romajizations, and has a theoretic support for katakana.


These images could also be helpful.