What is the weight of a priority mail envelope?

Ten 12.5x9.5 USPS Priority Mail envelopes weigh 14.9 ounces.  An ounce is 28.3495 grams.  How much does one envelope weigh?  This question also applies to USPS Priority Mail Express envelopes of the same size.

14.9 ounces times 28.3495 grams per ounce divided by 10 envelopes:

14.9 * 28.3495 / 10 = 42.24 grams per envelope.

Have you heard of "units analysis"?  It's a decent way to check your math when you do this kind of calculation.  You can ignore the numbers, but you have to remember that anything over itself (as in a fraction) is 1 and multiplying by 1 has no effect. So, applying that to the above, we have:

ounces times grams per ounce (g/o) divided by envelopes (e), or

o * g/o / e.  This puts ounces and grams in the numerator and envelopes and ounces in the denominator, and that allows us to "cancel out" the ounces (because they are in the numerator and the denominator), leaving us with grams per envelope.

When I get a receipt from Mailwerkz, my favorite place to send and receive packages, it shows the weight of the package I mailed.  This is very handy because I can convert it from pounds to grams and subtract the weight of the envelope to find out how much what I mailed actually weighed.