Comments: While you can do a polynomial curve fit of any order, you should have a good reason, possibly based on the physical phenomena behind the data, for trying a particular order. Blindly fitting a higher order polynomial is often misleading. The most common and trustworthy curve fit, by far, is the straight line. If you expect the data to have exponential relationship, convert the data to a log scale and then do a linear curve fit. The result is a lot more trustworthy than an arbitrary 6th or 10th order polynomial fit. As a rule of thumb, polynomial curve fits of order higher than 4 or 5 are rarely required.