Short answer: There is no scriptural “conversion” between Ayambil (often written Aayambil/Ambil) and Upvās. They are different types of tapas, each with its own vrati-rules and punya; Jain āgamas do not give an equivalence like “2 ambil = 1 upvās.”

• Upvās: full fast for about 24 hours (tradition-specific rules about water).
• Ayambil (Ambil): one very plain, tasteless meal in the day, without rich/tasty items.

Community “point charts” or informal counts sometimes compare fasts, but these are local customs, not from scripture. Follow the guidance of your own guru/saṅgh.

For a simple overview of Jain fasts, see:

• what are the main Jain fasts
• explain fasting methods