By the way you phrased your question, I know this isn't exactly what you want to hear (and ALOT of people ask the same question when they first get a dragon). You'll feed them as many is they can eat in 5-10 mins. Sometimes it's 10-15, sometimes it's 50-75 crickets. It's different for each dragon, their age, what else they ate, what mood their in and so on. There's no rule. Most new owners think the dragon's going to explode after a while. They usually eat more crickets then you'd think their stomach can even hold. But after a while they'll stop chasing them around and go bask, that's how you know when they're done.