The country dialling code for United States is +1or 001 (they're both identical).
If you want to make a call to United States from abroad, you have to dial the following country code +1 (or 001) followed by the national telephone number.
National telephone number: (201) 555-0123 (for local calls)
International telephone number: +1 201-555-0123 (for calling from abroad to United States)
Capital : Washington, D.C.
Population : 321 645 000 Inhabitants
Time : 2018-12-11 09:35
Time zone : America/Chicago