usps does weight have to be exact?
Weigh Your Item and Round Up USPS rounds up to either the next pound (lb) or ounce (oz). For example, if your package weighs 3 lbs 5 oz, it would be charged at the 4 lb-rate. If you have an item for shipping by First-Class Package® service that weighs 7.3 oz, it must be charged at the 8 oz-rate.