It depends on your country of residence, your nationality, the immigration officer in charge of your case and the visa category you are applying for. B1 and B2 visas are valid for a range of 1 to 10 years (depending on your citizenship and where you apply) and allow multiple entries to the United States.
Keep in mind: Visa validity and how long you are allowed to stay in the United States are two different things. For more info, click here.
The following table shows visa validity in number of months, by country:
