One critical component to controlling the cost of a PCB from the design stage is materials utilization.
The most common panel size is 18"x 24" and it's in your best interest to use as much of this space as possible.
A quick and easy tool for calculating best fit is KwickFit from MicroMeg.
Basic InstructionsPart Size
Enter in your single board or array size
Allow Part Rotations
Only check this if the array is tab routed or if the board is in single pieces. This avoids the requirement for jump scoring.
Enter 18 x 24
If this is in a scored array enter 0 in both fields. If this is routed enter 0.3" in both fields.
If this is a 1 or 2 layer board, enter 0.65 in all 4 fields. If this is a multilayer board, then enter 0.75 in all 4 fields. These are the most common panel border widths used in the industry.