The Current Visa Bulletin is available on the U.S. State Department Website.
First: (F1) Unmarried Sons and Daughters of U.S. Citizens: 23,400 plus any numbers not required for fourth preference.
Second: Spouses and Children, and Unmarried Sons and Daughters of Permanent Residents: 114,200, plus the number (if any) by which the worldwide family preference level exceeds 226,000, plus any unused first preference numbers:
A. (F2A) Spouses and Children of Permanent Residents: 77% of the overall second preference limitation, of which 75% are exempt from the per-country limit;
B. (F2B) Unmarried Sons and Daughters (21 years of age or older) of Permanent Residents: 23% of the overall second preference limitation.
Third: (F3) Married Sons and Daughters of U.S. Citizens: 23,400, plus any numbers not required by first and second preferences.
Fourth: (F4) Brothers and Sisters of Adult U.S. Citizens: 65,000, plus any numbers not required by first three preferences.