Depends where you are sending it
The price can vary a great deal depending on the type of 'kiloware' it is. It will be more if it is all commemorative stamps. The most would be high values with airmail stamps. The lowest would be definitives issued by a country such as the US, Great Britain or France.
.5 liters = 16.91 US fluid ounces.
For an envelope that weighs 5 ounces, you would need 5 Forever stamps. Forever stamps are typically for 1-ounce letters, so you would need to use multiple stamps to cover the additional weight.
5 US fluid ounces = 0.625 US cups
5 liters comes to 169.07 US fluid ounces @33.814 ounces per liter.
5 US fluid ounces = 147.87 ml
5 US fl oz is about 148mL
It costs $1.90, so 5 stamps (44¢ each) would cover it. That would be a waste of 30¢ though. I would just go to the post office and pay for the exact postage.
US nickels weigh 5 grams, which converts to 0.176 ounces.
how much are 5 1969 price of wales stamps worth
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.
It depends what country and how far you are sending it.