Answer:
Thousands; perhaps tens of thousands. It varies, of course. When the Earth passes through the path of an old comet, we have a "meteor shower", but even during normal times there are a very large number.
Most of them are the size of a grain of sand, and a "big" one can be as big as a grain of rice; perhaps even as big as a corn kernel. There are the rare giant meteors, of a few inches or even a few yards in diameter, that come along a few times a year, and VERY rarely, something big enough to punch through the atmosphere and do some major damage. For example, i 1908 a meteorite struck Siberia near the village of Tunguska, and caused an explosion as powerful as a nuclear bomb. It leveled miles of forests, and caused fires; the explosion was heard a thousand miles away!