Sorry, we currently do not support calculating fields.
In FormsCentral, you can use formulas in the response table to add together values in a response. For an example of this, you can fill out this form:
And you can see the response table for that form here:
I've created two columns that use different labels to add together the number fields in the form. You can mouse over a cell in those columns to see the formulas used.
Hope that helps!
Can you provide instructions on how to do this? We would like to use forms central for students/parents to order their annual band t-shirts. We need to calculate total number of shirts a student/parent orders and then multiply by cost per shirt. We could then use your Pay option for payments.