As of January 26, 2020.
This page is not meant to be a comprehensive list of current U.S. Postal Rates, rather, just the ones most commonly used by individuals. For a comprehensive list from the USPS, click here.
First Class (Retail)
| Product Letters (1 oz.) Letters additional ounces Letters (metered 1 oz.) International Letters/Postcards (1 oz.) Domestic Postcards Semipostal Stamps |
Price 55¢ 15¢ 50¢ $1.20 35¢ 65¢ |
The domestic Priority Mail Retail Flat Rate prices are:
| Product Small Flat Rate Box Medium Flat Rate Box Large Flat Rate Box APO/FPO Large Flat Rate Box Regular Flat Rate Envelope Legal Flat Rate Envelope Padded Flat Rate Envelope |
Price $8.30 $15.05 $21.10 $19.60 $7.75 $8.05 $8.40 |
The domestic Priority Mail Express Retail Flat Rate prices are:
| Product Regular Flat Rate Envelope Legal Flat Rate Envelope Padded Flat Rate Envelope |
Price $26.35 $26.50 $26.95 |
Large Envelopes (“flats”):
These should be bendable, by at least half an inch.
| Weight up to: 1 2 3 |
Price $1.00 $1.20 $1.40 |
| …and so on, up to 13 ounces |
“First-Class Package Service—Retail,” which the USPS calls “a lightweight expedited offering used primarily by businesses for fulfillment purposes,” is for non-bendable “flats.” It includes tracking, at about half the cost of Priority Mail. However, it is not easy to produce a table for this service, because the rate now ranges from $3.80 to $4.20 for up to four ounces, depending on distance. Higher weights are available, too.
To determine a domestic zone, use this tool on the USPS website. Choose the second tab, “Get Zone for ZIP Code Pair.” Here’s the rate chart: 
Thank you to VSC member Foster E. Miller III for his help on this article.
As far as I can tell, 1oz international letters and postcards increased to $1.20.
Very useful thread
Is there a rate for publishing materials like “books”?
Yes it is called “media mail,” and is cheaper but slower than other shipping services offered by the USPS. It also has restrictions: Chief among them is that there can be nothing resembling a letter or invoice enclosed. That’s why you’ll sometimes see a parcel with an envelope affixed on the outside, with its own postage: That’s the letter or invoice.
More on Media Mail can be found at shipping services about half way down the page.