Calculating Air Velocity at the outlet of a swept fan blade?

How do you calculate the velocity of the air being pulled through the fan blades? I am interested in finding the air's exit speed. I only have measurements of the area and geometry of the blades as well as the atmospheric pressure at sea level; from this I can derive volume if that is a necessary component in the equation. I Plan on using a variation of rotational speeds with the blade set to find different velocities and which range would be best for my project so how should I go about finding the velocity of the air itself as it exits the blade set? I need the velocity of the air for a component in a larger problem I am solving but have little knowledge in this area. Help will be much appreciated!