Is there a formula for this?

I want to determine how fast an object moves under psi and then convert it to mph and/or ft per sec. If I have something like a penny and psi is about 200lbs, how fast would it go?

When you say "how fast an object moves under psi" what does that mean to you?

I'm having some trouble envisioning what you're wanting to do here.

Yes, I agree with tom, we need some more information to determine what exactly you are trying to figure out and while the penny idea seems simple enough what is propelling it per say. Where as if you had a set degree of propulsion I.E. ballistics. As you will note lower barometric pressure results in lower drag. But humidity has the affect of reducing air density as well and should be considered hand in hand with the barometric pressure.

While these apply to a bullet, something propelled by an combustion engine would be another story. Think of it like a super or turbo charger on an car engine. The more the air is compressed the greater the quanity of oxygen available to burn fuel. Ask some top fuel dragster mechanics and they will have a in depth discussion with you about barometric pressure, if they have time.

So if you want help please post a more in depth description of what you are trying to figure out. And you will probably have some more help in the matter.

F/M=V

F-FORCE
M-MASS OF THE OBJECT
V-VELOCITY

Just off the top of my head.

Okay, if you're talking about how fast can you move an object through a tube with pressure behind it, you will of course be using that pressure as your driving force... then you have to take into account the coefficient of friction of the object against the walls of the tube, and the pressure ahead of the object in the tube.

If you're talking about a fixed force acting on the object and how much the pressure will cause decelleration, you will again have to find the coeficient of friction, only this time for the objects skin against air molecules that close together... from that you can find how fast you can move the object with different forces acting upon it...

We really need an example of this to know what youre asking here.