I think there's another topic with this same exact question. I don't remember the exact amount, but there was definitely a topic made just for this.
oh ok thank you
No topic was created as far as I can find Vash!
Hyperonion there is not really a way of telling, a block isn't a standard unit like a meter (or a megabyte!) As far as I'm aware we don't know how much of the Wii's internal memory is used for storage and therefore we can't give a value for this arbitrary unit!
Remember to always click the thanks button of those who help you! It makes them feel wanted:↓
http://www.wiiloaded.com/Wii-Memory-FAQ-t-3919-wii
^^ Should answer all of your questions.