Your answer depends on the origin location of the letter and its ultimate destination. If your point of origin is in the United States, you can review USPS postal rates, below.
Otherwise, you can find local postal rates at your local post office.
2
how many first class stamps does it take to mail a 4 oz letter and package
78 cents
1 oz letter to UK is .94
-2 and 1/2
what stamp amount is needed if the letter is 15 oz.?
3 it is 1 stamp/ounce as a rule of thumb
2 stamps. ! stamp is good for up to one ounce, 21 cents for second ounce.
You need one 44 cent stamp for a letter up to 1 oz. You can use any number of stamps as long as the postage total is 44 cents.
36 fl oz is 1064.65mL
From anywhere in the U.S. to the state of Georgia, a 1 oz letter will use one stamp.
One forever stamps pays for up to a one ounce letter. BTW, I think .06 oz. is impossibly light. Maybe you meant .6 or something else.