Cruise altitude is decided by what factors?

Usually Max Range and fuel consumption. If it is a short trip, the cruise altitude may be limited. Cruise altitude is determined by a number of factors, among which are winds, weather, length of flight, fuel economy, etc. Generally speaking, the higher a jet can fly, the more it will save in fuel. However, on shorter legs, an aircraft may not be able to reach the most economical operating altitude. Then, too, winds and weather can be major factors in selecting a lower than optimum cruise altitude.