How do you calculate new tax levy to pay for municiple services?
First, it depends of course on which type of tax is going to be used.
If your meaning as an addition to real property taxes: Take the amount budgeted to be raised and divide by the amount of property on the "grand list" to determine the rate. Convert to whatever unit amount is used there..generally mills.
Obviously some areas have certain changes or equalization adjustments they require that must be used too.