How many potato tubers in containers of different sizes?

[Hector]

How do you know how many spuds to plant? In this 2 by 2 looks like 9????
http://seattletimes.nwsource.com/ABPub/zoom/html/2002347127.html

I am thinking of making mine 3X 3 foot and I;m not sure how many ubers to put in?

Also, in these potato sacks what do you recommend?
http://www.marshalls-seeds.co.uk/potato-gro-sacks-x3-pid2036.html

[Hector]

[Tattieman]

In the 40 litre potato planter sacks I have 5 first earlies per sack. If I was putting maincrops in them I would probably just put 3 per bag. I think that gives you an average of 1 potato per 10 litres of compost but I have polypots that hold 17litres of compost and that is just perfect for 1 potato.
Hope that helps.

[Hector]

Thanks tattieman, very apt name too, for such good advuice :)