What formula should I use to calculate VAT?

This does not constitute professional tax advice. We strongly advise consulting a tax specialist to find out your specific obligations.

Grandville Printing charges VAT for orders that are fulfilled in any Grandville Printing location with an end-address in an EU member state.

You need to collect VAT on orders that have an end-destination in the EU, regardless of where they're fulfilled.

This is the formula you should use to collect VAT:

(Your retail price + shipping + services - discounts)*VAT rate %. Services include embroidery file digitization. 

The VAT rate percentage depends on the country that you're registered in and where the order is shipped. Take a look at each country's VAT rates here.