There are a number of variables other than weight. The overall size of the package will matter as well. A three ounce letter would cost 85 cents. If it is too thick, there is a surcharge and if it is a big envelope there may also be a surcharge.
1 but it depends on the weight of the package
How many stamps to STOCKHOLM
Depends where it's going to
1
if it weighs an ounce or less, three stamps.
3
20
If it is in the US, one stamp.
It takes 98 cents to send a letter to Brazil from the US
TWO US Forever stamps will suffice (USA to London post card)
usually none, but if it needs a stamp, just one stamp is needed.
Ohio is a state, one stamp.