Postal rates may be helpful in dating old covers (envelopes and folded letter sheets) however we caution you to carefully examine the rates and time periods involved. There may be many variables in determining the correct answer to your question. Not all the answers are on this page. There are many postal historians available who might help you.
        United States postage rates varied according to the distance a letter was to be carried from the post office where it entered the mail to its final destination. These “zone” rates were stable from 1816 (with a minor change in the 151 to 400 mile rate in 1825) to 1845. United States zone rates were modified in 1845 to reduce the number of zones to only two. Rates were adopted in 1847 for mail to or from the Pacific Coast and in 1848 for mail sent from one place in the west to another place in the west.
        There were “double” and “triple” rates as the letter’s size increased. There were ship fees which were also added (i.e. mail to Hawaii). The ship fee, including the ship rate on letters for delivery at the port of entry, were on a per letter basis, rather than weight.
        The United States issued its first postage stamps in 1847. Before that time, all domestic mail was “stampless” with the rates, dates and origin of the letter being either written by hand (manuscript) or sometimes in combination with a handstamp device.

Bassville Mississippi manuscript
postmark (1838). 25 cent rate.


Pendleton Hill Connecticut circular
postmark (1843). 10 cent rate.


HUDSON RIV. MAIL NY postmark
with US 5 cent stamp, letter dated 1849.
Note pen cancel (a.k.a “killer”)
Our first postage stamp.

        Goverment officials and local postmasters had the “franking privilege” so you might see a manuscript marking like this: “Free, John Calhoun, Sec of War.” This franking privilege was applied to mail being directed to them as well as mail sent from them.
        Manuscript postmarks were used after the United States Post Office issued postage stamps, the stamps themselves were first sent to some few post offices in major cities. The 1847 issue included both a 5 cent and a 10 cent stamp (below).

         

        Incidentally, world’s first postage stamp was the British 1840 Penny Black (below).

Penny Black

Colonial To 1782
        The British colonies in North America had no organized mail service in the early 1600’s. Postal service in the American colonies began in the private inns and coffee houses of seventeenth-century seaports. Inter-colonial mail was rare, and privately carried. Native Americans, slaves, and servants were all impressed to deliver or forward the mails. Commerical exchange within and between colonies was most often by boat along the eastern seaboard.
        While colonial postal system was ever so slow in developing, the roots were deep in British law. As Britain developed its own postal system, it eventually applied it system to the colonies.

Three British Acts that ultimately had effect on the colonies:

A Proclamation for the Setling of the Lre [Letter] Office of England and Scotland.
Proclamation of July 31, 1635, Patent Roll (Chancery) 11 Car 1.

Post Office Act, 12 Charles II, (1660)
A Post-Office erected and established

Post Office Act of 1710. 9 Anne.

        These Acts establish the government as the only lawful provider of the country’s postal system: in other words, a monopoly. The British monetary system of pounds, shillings and pence were the norm in the colonies, literally “coin of the realm,” but difficult to come by, so this pecuniary problem had a tendency to stifle the volume of letters mailed. The British appointed postmasters, established rates, and introduced postmarks. It was impossible to pay a British postmaster with Spanish “pieces of eight.”
        In 1639, the Massachusetts General Court established the first postal system in the colonies. Richard Fairbanks’ tavern in Boston was authorized as the official repository of mail, both local and from abroad.
        In 1673, Governor Francis Lovelace of New York established a monthly delivery system between New York City and Boston. While short lived, the post rider’s trail became known as the Old Boston Post Road.
        William Penn established Pennsylvania’s first post office in 1683.
        In 1691, Andrew Hamilton was appointed postmaster general for North America. In April 26, a 1699 letter from Andrew Hamilton to “Right Honourable the Lords Com. of his Majesty’s Treasury” notes inland postage rates.

Where the distance from New Yorke to Boston is within 80 miles the postage	6d.
Where the distance exceed 80 miles and within 150	9d.
Postage to and from Boston to New Yorke being 300m.	12d.
To and from Boston to Jersey 370 miles	18d.
To and from Boston and Philadelphia 390 miles	20d.
To and from Boston to Annapolis in Maryland 550m.	36d.
To and from Boston and James Towne in Virginia 680m.	42d.
To and from New Yorke to Annapolis 250 miles	24d.
To and from New Yorke to James Towne 380 miles and many broad and dangerous Bays and Rivers to be Ferryed over.	30d.

        From the “Postal Services in the Colonies, 1592-1775.” The Southern Philatelist 2, no. 6 (March 1891): 87-8. The complete article follows:

        The first Parliamentary Act for the establishment of a postoffice in the English American Colonies was passed in April, 1692, when a royal patent was granted to Thomas Neale for the purpose. He was to transport letters and packets “at such rates as the planters should agree to give.”
        Rates of postage were accordingly fixed and authorized, and measures were taken to establish a postoffice in each town in Virginia, when Hale began his operations. Massachusetts and other Colonies soon passed postal laws, and a very imperfect postoffice system was established. Neale’s patent expired in 1710, when Parliament extended the English postal system to the Colonies. The chief office was established in New York, where letters were conveyed by regular packets across the Atlantic.
        A line of postoffices was soon after established on Neale’s old routes, north to the present City of Portsmouth, N.H., and south to Philadelphia, and irregularly extended a few years later, to Williamsburg, Va. The post left for the South as often as letters enough were deposited to pay the expense. The rates were fixed, and the post-rider had certain privileges to travel. Finally an irregular postal communication was established with Charleston.
        In 1753 Dr. Franklin was appointed Deputy Postmaster-General for the Colonies. It was a lucrative office, and he held it until 1774, when he was dismissed because of his active sympathy with the colonists in their quarrel with the Ministry. For a while the colonial postal system was in confusion. William Goddard, a printer, went from colony to colony, making efforts to establish a “Constitutional Postoffice,” in opposition to the “Royal Mail.”
        When, in 1775, almost every vestige of royal power was swept from the Colonies, the Continental Congress appointed (July 26) Dr. Franklin Postmaster-General. In the autumn of 1776, when Independence had been declared, and Franklin sailed for France, the whole number of postoffices in the United States was 75; length of post routes, 1,875 miles; revenue for about fifteen months, $27,985; annual expenditures, $32,142.

        Benjamin Franklin, who was appointed postmaster of Philadelphia in 1737, served as a deputy postmaster general for all the colonies from 1753 to 1774. After the start of the American Revolution, he was appointed postmaster general of the colonies. During his tenure in 1775-76 he laid the foundations for the United States postal service. He greatly increased the number of post offices, started a packet mail service to Britain, and introduced the use of stagecoaches to carry the mails.

1782 to 1816

        On September 26, 1783, George Washington appointed Samuel Osgood of Massachusetts as the first Postmaster General under the Constitution. At that time the post office was a bureau of the Treasury Department. When Osgood took office there were only 76 post offices and less than 2,400 miles (3,900 kilometers) of post roads.
Continental Congress, Ordinance of October 18, 1782.
(23 Journal of the Continental Congress)
During the American Revolution, the Continental Congress established its own postal service and modeled postal monopoly provisions on Queen Anne’s Act of 1710.
United States Congress
Act of February 20, 1792, ch 7, 1 Stat.. 232 (2d Congress, 1 Session)

Single rate:
Not exceeding 30 miles, 6 cents
over 30, not exceeding 60, 8 cents
over 60, not exceeding 150, 12 cents

        During the War of 1812, in order to generate much needed revenue to pay for the war, the United States increased its postal rates. The regular postal rates were increased by 50% in February 1815, and were in effect until 31 March 1816 when the rates were repealed.

31 March 1816 ~ 31 June 1845

Single letter rate. A single letter was defined by the number of letter sheets until 1827, and thereafter by weight, one ounce being a single letter until 1845, and one half ounce thereafter.
Not over 30 miles, per letter sheet.: 6 cents.
31 to 80 miles, per letter sheet.: 10 cents.
81 to 150 miles, per letter sheet.: 12½ cents.
151 to 400 miles, per letter sheet.: 18½ cents.
Over 400 miles, per letter sheet.: 25 cents.
1827
Not over 30 miles, per oz.: 6 cents.
31 to 80 miles, per oz.: 10 cents.
81 to 150 miles, per oz.: 12½ cents.
151 to 400 miles, per oz.: 18¾ cents, (effective 1 June 1825).
Over 400 miles, per oz.: 25 cents.

1 July 1845 ~ 1847

(Old rates eliminated.)
Not over 300 miles, per ½ oz.: 5 cents. Collect: 5 cents.
Over 300 miles, per ½ oz.: 10 cents. Collect: 10 cents.
Drop letters: 2 cents.

Added 1847 ~ 1848

To or from Astoria Oregon or the Pacific Coast, per ½ oz.: 40 cents. Collect: 40 cents.
Along the Pacific, per ½ oz.: Collect: 12½ cents.

1 July 1851

(1847-1848 rates eliminated.)
Up to 3000 miles, per ½ oz.: 3 cents. Collect: 5 cents.
Over 3000 miles, per ½ oz.: 6 cents. Collect: 10 cents.
Drop letters: 2 cents

30 September 1852

Up to 3000 miles, per ½ oz.: 3 cents
Over 3000 miles, per ½ oz.: 6 cents
Drop letters: 2 cents

1 April 1855

(Elimination of “collect” option. Prepayment mandatory)
Up to 3000 miles, per ½ oz.: 3 cents
Over 3000 miles, per ½ oz.: 10 cents
Drop letters: 2 cents

1 July 1863

To all parts of the United States, per ½ oz.: 3 cents.

1 October 1883

To all parts of the United States, per ½ oz.: 2 cents.

1 July 1885

To all parts of the United States, per 1 oz.: 2 cents.

1 October 1896

Rural Free Delivery begins.

2 November 1917

(WWI emergency rate increase.)
To all parts of the United States, per 1 oz.: 3 cents.

1 July 1919

(WWI emergency rate increase rescinded. Pre-war rate restored.)
To all parts of the United States, per 1 oz.: 2 cents.

6 July 1932

(Rate increase to offset depression costs.)
To all parts of the United States, per 1 oz.: 3 cents.

1 August 1958

To all parts of the United States, per 1 oz.: 4 cents.

Winchester Advertising Envelope 1903