IR sensor distance convert

Hello. How to convert data from Sharp IR gp2y0a41sk0f-4-30 to centimeters ?I use this code:

numberOfSensors 2
int ir1 = A1;

void setup() {
Serial.begin(38400);
}
void loop() {
float volts = analogRead(ir1)0.0032226;
float distance = 12.3
pow(volts, -1.10);
Serial.print(distance);

delay(250);
}

But i have error by 2cm. I try change coefficient 12,3 but the error is the same .

You are calculating ‘volts’ based on a 3.3V analog reference (0.0032226 = 3.3/1024). You are not using analogReference(EXTERNAL) so are you running this on a 3.3V Arduino?