JotForm is a free online form builder which helps you create online forms without writing a single line of code. No sign-up required.
We believe that if one user has a question, there could be more users who may have the same question. This is why many of our support forum threads are public and available to be searched and viewed. If you’d like help immediately, feel free to search for a similar question, or submit your question or concern.
Since the form is not a spreadsheet, I don't think the form can perform calculation the same as in Excel (Or use Excel formulas). But you can use Calculation field to perform almost any type of computation (Use functions like squaring, rounding..).
Please take a look a the calculation guides from this link: http://www.jotform.com/help/chapter-9-Form+Calculations.