Hi Rati/Aravind,
I make Idlis at home every week. I live in USA and I've got ULTRA pride wet grinder. The below is the measurement I use:
Laxmi Ponni Raw Rice--- 1/2 cup
Laxmi Boiled Raw Rice-- 3.5 cups
Urad Dal (Ulutham Parupu in tamil) -- 3/4 cup
Aval --- One handful (optional---for extra softness)
Methi seeds (Venthayam) -- 2 T-spoons.

Soad Raw Rice and Boiled rice together (A) .....and the remaining ingredients together (B). Grind the B part first and then the A part. This makes idli softer.
ALL THE BEST