Okay, I just contacted the vet and the dosage is as follows in case anyone else is interested:

6mg/per kg which is 6mg per 2.2lb
A large sized Revolution for dogs (colour Teal) comes in tubes that are 4ml in size and have 240mg per tube which works out to 60mg per ml.

I'm trying to help a woman who is is rescuing a stray cat that seems to be infested with fleas and mites and she thinks it is about 6 or 7 pounds so 20mg should do it which works out to about a third of a ml.

I knew my old vet used to use this method and that it was safe but I just couldn't remember the correct dosage. A shelter I used to volunteer at always bought the Revolution for dogs in 6 packs and it would provide roughly 72 doses for cats which really affordable.

Revolution in Canada is by prescription only to ensure that the cat is healthy and doesn't already have heartworm since it treats that as well but we do not have heartworm in this part of the province. And this kitty is in horrible shape and the woman helping her doesn't have any money and I happened to have some large dog Revolution on hand and really wanted to help her.

My next goal is to try and help her get the cat spayed!

Thanks for your posts everybody!