how meny oz.for one us stamp?

The United States Postal Service (USPS) bases pricing of mail on a combination of size, weight, shape, destination, item valuation, and class of service selected.

Using a sender selected envelope which does not exceed a maximum length of 11-1/2 inches, maximum height of 6-1/8 inches, or maximum thickness of 1/4 inch, USPS First-Class Mail service will send from one United States location to another a one ounce weight letter for $0.49. The price increases as the weight goes up.

mailing 1 ounce - $0.49 (one Forever stamp)

mailing 2 ounces - $0.70 (two Forever stamps)

mailing 3 ounces - $0.91 (two Forever stamps)

can use a larger envelope - maximum length of 15 inches, height of 12 inches, and thickness of 3/4 inch

mailing 4 ounces - $1.61 (four Forever stamps)

mailing 5 ounces - $1.82 (four Forever stamps)

mailing 6 ounces - $2.03 (five Forever stamps)

mailing 7 ounces - $2.24 (five Forever stamps)

mailing 8 ounces - $2.45 (five Forever stamps)

mailing 9 ounces - $2.66 (six Forever stamps)

mailing 10 ounces - $2.87 (six Forever stamps)

mailing 11 ounces - $3.08 (seven Forever stamps)

mailing 12 ounces - $3.29 (seven Forever stamps)

mailing 13 ounces - $3.50 (eight Forever stamps)

https://www.usps.com/

https://www.usps.com/ship/first-class-mail.htm

Use the USPS Calculation page link below to determine the exact postage for the weight and size item you are mailing. Enter the destination, select using a box for mailing, enter the weight, and get the required postage amounts.

http://postcalc.usps.com/

It depends on the value of the stamp.