Is there a way to calculate the relationship between a set of values?
When I see a question like this, my first thought is to use curve fitting/regression. I don't know how familiar you are with regression techniques -- it might be worth visiting your favorite intro to stats text and review linear regression techniques.

In Excel, I find the easiest way to curve fit data is to use the LINEST() function http://office.microsoft.com/en-us/ex...in=HA010277524

Often the hardest part of curve fitting is deciding what form of equation to use. This will usually be based on your knowledge of the underlying physical process being modeled and the expected equation that should use.

Your data look fairly linear, without more information I would suggest a simple straight line y=mx+b, for which examples are readily given in the help file.

Once you have the equation and the parameters for the equation, it should be easy to create a block of cells where you can input any T and get any P.