const int sensorIn = A0;      // pin where the OUT pin from sensor is connected on Arduino
int mVperAmp = 25;           // this the 5A version of the ACS712 -use 100 for 20A Module and 66 for 30A Module
int Watt = 0;
double Voltage = 0;
double VRMS = 0;
double AmpsRMS = 0;


void setup() {
  Serial.begin (9600);
  Serial.println ("ACS712 current sensor");
     
}

void loop() {

  Serial.println ("");
 
  Voltage = getVPP() -0.01;
  VRMS = (Voltage/2.0) *0.707;   //root 2 is 0.707
  AmpsRMS = (VRMS * 1000)/mVperAmp;

  Serial.print(AmpsRMS);
  Serial.print(" Amps RMS  ---  ");
  Watt = (AmpsRMS*230/1.0);      // 1.3 is an empirical calibration factor
  Serial.print(Watt);
  Serial.println(" W");
}


float getVPP()
{
  float result;
  int readValue;                // value read from the sensor
  int maxValue = 0;             // store max value here
  int minValue = 1024;          // store min value here
 
   uint32_t start_time = millis();
   while((millis()-start_time) < 1000) //sample for 1 Sec
   {
       readValue = analogRead(sensorIn);
       // see if you have a new maxValue
       if (readValue > maxValue)
       {
           /*record the maximum sensor value*/
           maxValue = readValue;
       }
       if (readValue < minValue)
       {
           /*record the minimum sensor value*/
           minValue = readValue;
       }
   }
   
   // Subtract min from max
   result = ((maxValue - minValue) * 5.0)/1024.0;
     
   return result;
}

...
  VRMS = (Voltage/2.0) *0.707;   //root 2 is 0.707
....

...
    Watt = (AmpsRMS*230/1.0);
....