Depends. It can range from 355knots (low altitudes) till only about 220knots (very high altitudes and slow cruise)
The cruising altitude of Boeing 747 is 30,000 feet.
Cruising speed of most fighters is around 650 mph.
567 mph
The cruising altitude of a 747 depends on weather conditions, weight of the aircraft, and the amount of traffic on the other flight levels. Its average cruising altitude is around 33,000 feet.
Maximum speed: 590 mph at 27,000 ft. Cruising speed: 520 mph at 34,000 ft.
585 mph cruising speed
The service ceiling of a Boeing 747 is 43,000 ft. The maximum is 45,000 ft.
A 747 typically cruises at 0.84 mach/560 nautical miles per hour.
The cruising altitude of a normal commercial jet airplane today is around 12,000 m (35,000 ft).
Cruising speed is around 570 mph. Maximum speed is around 614 mph.
The Boeing 747-8I series has a cruising speed of 570 mph (Mach 0.855). It's maximum speed (both the 400 and 8I series) is 614 mph (Mach 0.92).
With zero wind and depending on the model the average 747 will cruise at .82 mach. The ground speed will increase proportionally with the tail wind.