Mega-UK - How many PCB Boards can I etch with Ferric Chloride?

How many PCB Boards can I etch with Ferric Chloride?
1 litre of Ferric etching solution will hold 65g of copper before it is saturated. With standard 35 micron copper boards you will normally be able to process approximately 12 panels 10x12 with 5 litres of Ferric assuming you are removing two thirds of the copper from each panel.