Aeronautical Information Manual (AIM), page 159
12/10/15 AIM Section 3. Class G Airspace 3-3-1. General 3-3-3. IFR Requirements Class G airspace (uncontrolled) is that portion of airspace that has not been designated as Class A, a. Title 14 CFR specifies the pilot and aircraft Class B, Class C, Class D, or Class E airspace. equipment requirements for IFR flight. Pilots are reminded that in addition to altitude or flight level requirements, 14 CFR Section 91.177 includes a 3-3-2. VFR Requirements requirement to remain at least 1,000 feet (2,000 feet Rules governing VFR flight have been adopted to in designated mountainous terrain) above the highest assist the pilot in meeting the responsibility to see and obstacle within a horizontal distance of 4 nautical avoid other aircraft. Minimum flight visibility and miles from the course to be flown. distance from clouds required for VFR flight are contained in 14 CFR Section 91.155. b. IFR Altitudes. (See TBL 3-1-1.) (See TBL 3-3-1.) TBL 3-3-1 IFR Altitudes Class G Airspace If your magnetic course And you are below (ground track) is: 18,000 feet MSL, fly: 0 to 179 Odd thousands MSL, (3,000; 5,000; 7,000, etc.) 180 to 359 Even thousands MSL, (2,000; 4,000; 6,000, etc.) Class G Airspace 3-3-1
Page 159 of the Aeronautical Information Manual (AIM.pdf)
AIM: Official Guide to Basic Flight Information and ATC Procedures