Get the data / fan curve from the manufacturer of the fan.
What ever duct work, dampers etc. that is connected to the fan will determine the static pressure.
The velocity of the air in the duct will be determined by the duct size and how much air you are running through it.
Higher flow = higher static and velocity
The way you word your question makes me think that you are trying to size a fan for a system. If so then you need to get the design data for the system or design the system considering required volume, static pressure and friction loss from the duct work and maximum velocity in the duct (small duct and high velocity = noise)then select your fan based on the volume / horsepower / power requirements from a manufacturer catalog.