If you are not a web/JavaScript developer but want to have a simple customized online formula calculator for your visitors, check this site out:
https://jscalc.io
How to use:
Example embeddable calculator form in this article:
What about custom formulas & calculator styles?
If you want something like this instead, feel free to contact me at http://webflowexpert.com
(the design/colors can be customized to your theme/design.)
Seen on Community Solar Website