"Luty jest krótszy niż styczeń."

Translation: February is shorter than January.

[Tom873317]

When do you use niż vs od?

[mihxal]

They are interchangeable in comparisons but with "niż" you should use Nominative and with "od" - Genitive.

[Tom873317]

Dziękuję. Is "niż" then a conjunction, like in English where "than" is treated as a conjunction, as in "He is taller than I (am)" instead of "He is taller than me"?

[Jellei]

Yes, it is a conjunction.