How to convert ADC Analog from MQ3 Sensor to ppm?

Hi. I'm a bit confused about how to convert this ADC Analog to PPM with MQ3 Sensor.. The default result is about 200 - 300, i'm just very confused about this result. Which is good to know the calculation of calibration with that result. I just dont know how to calculate it, or if there any formula to get the PPM from that ADC analog result, please tell me.. Thanks in advance! :D

p.s: remind me if my thread is in wrong subforum. im newbie here. thanks! :D

That is not possible with a formula. The sensor is a chemical-electrical sensor, and it's resistance depends on the gasses. But the resistance varies a lot. I have written about calibrating here : http://arduino.cc/playground/Main/MQGasSensors