Generally, the more serious the theft crime, the more likely it will be charged as a felony. For example, if the item that is taken is valued at $950 or less, then the crime is considered petty theft according to California's regulations. Yet, if the amount is more than $950, you likely will be convicted of grand theft, which can be charged as either a misdemeanor or a felony.
However, under some circumstances, the property's value is not even considered. For instance, if you commit grand theft of a firearm, the offense is always a felony.