Create Basic Form Based Calculator

I am looking for a simple calculator that can be created for embedding onto my website. The calculator should look like a form with two entry fields (variables) and one output field. The CSS can be taken from our existing form styling on our website and matched accordingly.

The Fields Are As Follows:
[FIELD 1] Vessel Capacity In Litres
[FIELD 2] Feed Water TDS
= [OUTPUT] Total Capacity In Litres

[OUTPUT] is calculated by [FIELD 1] * 30,000 = [CALC 1]
[CALC 1] / [FIELD 2] = [OUTPUT]

Please feel free to get in touch if you require further information, however I have tried to make the calculation steps as clear as possible.