In Jain Dharma, Upwas and Ekashna (Ekasana) are two different types of tapa, so they are not converted into each other.

• Upwas (उपवास) = full fast for the day

- No food for the whole day (usually sunrise to next sunrise). - Depending on pachkhan, only boiled water may be taken, and sometimes even that is stopped.

• Ekashna / Ekasana (एकासन) = one meal only

- You eat once in the day, in one sitting, at one place. - This is not a full fast; it is a lighter tapa than Upwas.

So in simple words:

> 1 Upwas = 0 Ekashna > If you truly do Upwas, you are not doing any Ekashna that day.

In some special long taps (like Samvatsari tapa etc.), scriptures may compare: 3 Upvas = 12 Ekasana, etc., but that is only for counting that particular tapa, not a general rule for daily life.

You can read a detailed explanation here