Your question is a bit imprecise, and can be interpreted in quite a few ways. I'm going to presume that what you mean is

"How many Americans that were killed or wounded during World War II were killed or wounded before the atomic bombs were dropped?"

If that is indeed your question, than the answer is the vast majority of them. Less than a week elapsed between the second bomb was dropped and the Japanese announced their surrender. While Americans continued to die during that period, the lion's share of casualties had already occurred by that point. About a million total casualties were suffered, including killed, wounded, missing, or otherwise harmed (out of which a little less than 300,000 were killed, and a little more than 600,000 were wounded).