Cabin capacity is the number of seats available. If there are too few seats too many potential passengers are turned away, potential revenue is not realised and the proper service is not provided to the travelling public. If there are too many seats a lot of them will be unused when demand is low and costs will be high in relationship to revenue.

Cabin capacity is a consideration when aircraft are being procured but at that stage it need not be calculated very precisely. Once the aircraft is in service quite small adjustments may make the difference between profit and loss, a particular problem being where to divide the cabin between the different classes.