Let me get in this tread.
I did a project to monitor AC voltage.
I check your circuit, it look OK, as long the V out is not over 5 V.
So, To figure this out, you need this :
1. What is the voltage at that output of your circuit ? example : 3 V
2. What is the AC main voltage in rms ? example : 122 V
3. What is the A Vref voltage ? example : 5 V
So let calculate the ratio. 122 / 3 = 40.6666667
Let calculate a "step" value : 5 V / 1023 = 0.004887585 V
So Vin is the 3 V at the analog pin and 3 V is : 614 = value = analogRead( Vin );
Let do a code :
value = analogRead( Vin );
Vac = ( float (value) * ( 5.0 / 1023.0 ) ) * ( 122.0 / 3.0 );
Serial.print( Vac, 3);
Any question ?