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
1
if it weighs an ounce or less, three stamps.
3
20
If it is in the US, one stamp.
For a 5-ounce package, you would need to use enough stamps to cover the postage cost. In the US, the current rate for each additional ounce in a package is $0.20. Therefore, you would need to calculate the postage cost based on the total weight of the package (5 ounces) and then affix the appropriate number of stamps to cover that cost.
TWO US Forever stamps will suffice (USA to London post card)
It takes 98 cents to send a letter to Brazil from the US
usually none, but if it needs a stamp, just one stamp is needed.
Ohio is a state, one stamp.