What grade stainless?

What thickness?

What Joint configuration?
      If Fillet, flat or horizontal orientation
      If Groove is there a bevel?
      If Groove is it plate or pipe?

What travel speed (inches per minute) ?

What size cup/nozzel?

What is the stickout?  (length electrode extends from end of nozzel to point of electrode)

What is your tungsten diameter?

What is your current range measured in Amps?

Are you employing a trailing shield?
     If you employ a trailing shield is it integrated into the cup/nozzel?

Do you mean to ask, what flow rate?
Flow rate is the important shielding gas variable.
You need a flow meter, the type with a floating ball is very common and works well.
These types of flow meters are slightly affected by pressure, and generally are calibrated to be used at 30 psig.

There are flow meters that consist of an precise orifice, where flow rate is determined by pressure.

Vscid,

I Googled "gas flow rates for GTAW" to get you a simple, concise answer to your question.  There are a number of interesting hits, but the following was near the top.

www.amtonline.com/publication/article.jsp?pubId=1&id=1685

Gas Flow Rate

Setting a proper gas flow rate is another important element to successful GTAW. Contrary to what may seem to be common sense, more isn't better. If you are welding in a flat position, a flow rate of about 15 to 20 cubic feet per hour (CFH) is typically adequate. For overhead welding, you can start at about 20 CFH and increase the flow by small adjustments of about 5 CFH if necessary.

So why is too high a flow rate a bad thing? Well, if the gas flows out of the torch at too high a velocity, it ends up bouncing off the surface being welded and starts a swirling motion parallel to the torch cup called a venturi. This venturi effect will suck air into the gas flow, creating an impure weld atmosphere. This results in pinholes in the weld.

Note:  the 20 CFH corresponds to about 10 L/min for our metric users.
Hope this helps.