on Feb 4, 2016 at 3:40:49 pm Last Edited By Kalle Kannisto on Feb 4, 2016 at 3:45:43 pm
The artboard size doesn't really matter -- as long as it is larger that the artwork -- rather the size of the artwork itself. But if you want to be on the safe side, make the artboard that size (19.35cm x 19.35 cm) as well. The main thing to ensure is that the artwork itself isn't larger than that. I'd say it would be simplest to make the artboard the same size, then you can easily see if your artwork fits inside it.
In such a case I usually make the artboard the smallest US or international paper size that accommodates the artwork (such as letter size or A4), depending on where the customer is based. This obviously applies only in those situations where the paper size has no bearing on the trimming of the final product.