volatile long pulse; //pulse variable
float volume; //volume variable
const float calibrationFactor = 0.307; //calibration formula

in your setup()

attachInterrupt(digitalPinToInterrupt(FLOW_SENSOR_PIN), increase, RISING); // Attach interrupt to the flow sensor pin

void increase() {
    pulse++;
}  //function for rising pulse count 

// Function to recalculate volume based on pulse count
void updateVolume()
{
    const float calibrationFactor = 0.307;
    volume = calibrationFactor * pulse;
}