'morning there!   Well the general rule of thumb for stocking is for the first goldfish 20 gallons, and for each additional goldfish after that 10 more (gallons, not fish). Soooo, long term, for a 40 gallon tank 3 goldfish or less would probably be ideal. The reason goldfish need so much room is because they grow incredibly fast (at least an inch a year) and run out of room quite quickly. So though 3 goldfish that are each an inch or so long initially seems like understocking, keep in mind they don't stay that size. Fancy goldfish can grow anywhere from 6-8 inches long, sometimes even bigger. Not only that, but they also produce massive ammounts of ammonia, which can quickly poison the fish in a smaller space. Proper stocking will enable your fish to live long, happy, healthy lives and you to enjoy a relaxing tank, without all the stress caused by overstocking/bullying/frequent illness. Also, one thing I would add is that too small of a tank with too many fish causes stunting. This means that the body of the goldfish stops growing, but the organs do not, spelling death out for your friends. Not good.  So do it right the first time and don't put too many in there.

Hope this helps and good luck with your tank.  

Hahaha well the bigger the better, but 40 gallons is the perfect size for just a few. So you're right, if you want a large crew of goldies you will need an ark. 

Keep us posted on how everything goes with your new tank. 

I am so glad I came on this forum prior to buying my set up and fish, I had no idea, (regarding the size of tank to fish ratio) and I'm sure the people at the store wouldn't have a clue.

I'm looking at getting the tank in the next couple of weeks.

Note that you need to let the tank cycle before you add the fish! There's more info on that if you search the forum

yeah we should draw up a hierarchy of needs in relation to pet stores, we have the top and bottom parts already drawn up, $ at the top and animal welfare at the bottom....