Thank you, this is exactly what I was looking for. The highest cost from the electric company here is 32.8 cents per kWh during peak demand. With your formula, it would cost me 0.78 dollars per hour during peak demand.
As a part-time woodworker, if I run my Shapeoko for 15 hours per week. My total cost is estimated to be $46.80 per month. I am going to make sure this cost is reflected in my overhead.