It is actually normal for brand new and modern cars to consume oil.
There is no set number, but as a rule of thumb, it's often agreed that up to about 1 quart or 1 litre of oil per 1000 miles (e.g. out of 6L of oil from the oil pan) is considered to be an entirely normal oil consumption rate; on the other hand, more than 1L per 1000 km is probably too much of an oil consumption.
As others mentioned, this is not to be confused with oil leaks, where the oil leaks onto the ground from beneath the engine -- no such oil consumption should be considered as normal.