The hole density stands for the number of holes per dm² board surface. This number is usually around 600 holes/dm² for a standard double sided board. However smaller component size and denser circuits on ever smaller board surfaces have driven it up.
This density is linked to the costing factor for the drilling of the PCB. The more holes that need to be drilled the longer the board stays on the drilling machine and the more Tools (drill bits) need to be used.
As long as the hole density does not exceed 999 holes/dm², this factor will not affect the pricing. Above a small addition to compensate for the extra drilling cost will be calculated.
The hole density parameter can be found in the calculator – order details – Board technology.