The United States Postal Service prices mail by a small number of decisions the sender makes: the service (how fast), the shape (letter, flat, or parcel), the weight, and the destination zone. The prices change — usually each July — and the schedule in force today is the 13 July 2025 schedule, which raised the Forever stamp from 73¢ to 78¢ and the metered letter rate from 69¢ to 74¢, with larger rises on parcels. This guide explains the classes and the boundaries, states the July 2025 figures for the common cases, and names the check for everything else: the prices on usps.com, which are the only current figures, because this guide does not track rate changes. Postage and shipping are different subjects — this guide covers postage, the USPS retail and commercial mail classes; parcel shipping by private carriers, with their own zones and surcharges, is a separate calculation.

The classes: First-Class, Priority, Express, Ground Advantage

First-Class Mail is the default for letters, flats, and light parcels: delivery in 1–5 business days, by weight and shape, with no guaranteed date. Priority Mail is the expedited parcel service: 1–3 business days, flat-rate boxes available (one price whatever the weight, up to 70 lb), free boxes, and included tracking and insurance up to $100. Priority Mail Express is the fastest: overnight to most addresses, guaranteed date with a money-back guarantee, and the only service with a guaranteed delivery date. USPS Ground Advantage is the economical parcel service: 2–5 business days, priced by weight and zone, and the successor to the old Parcel Post and First-Class Package services, which it absorbed. Media Mail is the cheapest of all for books, media, and educational material — slower, restricted in contents, and subject to inspection, which is the price of the discount.

The class decision is a trade between speed, price, and guarantee, and the guarantee is the distinction that matters: Express guarantees a date, Priority estimates a range, Ground Advantage estimates a longer range, and First-Class estimates the longest. A letter that must arrive by a date needs Express or a service with a guarantee; a letter that must merely arrive needs First-Class. The postage calculation on this site prices the classes from the weight, shape, and zone entered, and the July 2025 schedule is the schedule it should be checked against.

Letters, flats, and parcels: the boundaries that set the price

Shape is priced before weight. A letter is rectangular, at least 3½ × 5 inches and no more than 11½ × 6⅛ inches, no more than ¼ inch thick, with an aspect ratio (length divided by height) between 1.3 and 2.5 — the envelope proportions. A flat (large envelope) is larger than a letter in any dimension, up to 15 × 12 inches and ¾ inch thick, and is priced by weight in ounce steps at a higher rate than a letter. A parcel is anything thicker, more rigid, or more irregular, and is priced by weight and zone. The boundaries are enforced by the mailpiece’s dimensions as presented: an envelope ½ inch thick with a rigid object inside is a parcel, whatever the sender calls it, and a non-machinable letter — square, rigid, or with a clasp or string — carries a non-machinable surcharge on top of the letter price.

Weight ends letter pricing at 3.5 oz: a letter over 3.5 oz prices as a flat, and the jump is larger than the ounce steps that precede it, because the flat rate starts from a higher base. The July 2025 letter prices are 78¢ for 1 oz (Forever stamp), $1.07 for 2 oz, $1.36 for 3 oz, with the metered 1 oz rate at 74¢ and each additional ounce at 29¢. The Forever stamp’s value is its convenience: bought at 78¢, it mails a 1 oz letter forever, whatever the rate rises to — which is why a drawer of Forever stamps bought years ago is a small hedge against rate rises, and why the stamp’s name is literal.

Zones, retail vs commercial, and the parcel price

Parcels are priced by zone: the distance between the origin and destination ZIP codes, in zones 1–9 (zone 1 local, zone 9 cross-country, with Alaska, Hawaii, and territories on their own zone logic). Letters and flats are not zoned — a letter costs the same to any US address — which is why the letter/flat boundary matters so much: crossing it introduces zone pricing. Commercial prices — bought online through Click-N-Ship, a postage meter, or an approved vendor — are lower than retail counter prices for parcels, by amounts that grow with weight and zone, and the difference is the reason regular shippers never pay retail. Dimensional weight (the parcel’s volume, not its scale weight) prices large light parcels: when the dimensional weight exceeds the actual weight, the dimensional weight governs, and the divisor the USPS uses is published in the pricing schedule.

The July 2025 rises fell unevenly: Priority Mail +6.3%, Ground Advantage +7.1%, Parcel Select +7.6%, Express unchanged, and the letter rises (78¢/74¢) were the smallest in percentage terms. The pattern — parcels rising faster than letters — reflects the cost structure: parcels are handled more, transported further per piece, and delivered to the door, while letters are machined in bulk. A shipper whose parcel volume is regular should price on the commercial schedule and the zone table, not on the retail counter price, and should re-check after each July’s rate change, because the zone boundaries and the dimensional divisor change with the schedule.

Extras: tracking, insurance, signatures, and certified mail

Tracking is included with Priority Mail, Express, and Ground Advantage, and available as an add-on for First-Class parcels. Insurance is included to $100 with Priority Mail and Express, and purchasable above that and for other classes, with the declared value as the coverage limit and the receipt as the claim evidence. Signature confirmation and adult signature add a signature on delivery; certified mail adds proof of mailing and proof of delivery, with a return receipt (green card or electronic) as the evidence — the service used for legal notices, tax filings, and anything whose delivery must be provable. Registered mail is the most secure: chain-of-custody handling, locked containers, and the highest insurance limits, for valuables and irreplaceable documents.

The extras are priced per piece, on top of the postage, and they are the difference between “sent” and “proved sent”: a certified letter’s return receipt is evidence in a dispute in a way a tracking scan is not, because the receipt is signed by the recipient and returned to the sender, while tracking shows delivery to the address. For a deadline that turns on mailing — a tax return, a legal filing — the postmark and the certified receipt together are the proof, and the cost of the extra is negligible against the cost of missing the deadline.

Frequently asked questions

How much does it cost to mail a letter in 2025?

From 13 July 2025, a 1 oz First-Class letter costs 78¢ with a Forever stamp, or 74¢ metered. Each additional ounce is 29¢: a 2 oz letter is $1.07, a 3 oz letter $1.36. Above 3.5 oz, letter pricing ends and the item prices as a flat or parcel. Check usps.com for the current schedule — rates change, usually each July.

What is the difference between a letter and a flat?

Size and thickness. A letter is up to 11½ × 6⅛ inches and ¼ inch thick, with an aspect ratio between 1.3 and 2.5. Anything larger in any dimension, up to 15 × 12 inches and ¾ inch thick, is a flat (large envelope), priced by weight at a higher rate. Anything thicker, more rigid, or more irregular is a parcel, priced by weight and zone. A non-machinable letter — square, rigid, or with a clasp — carries a surcharge.

What is the cheapest way to send a parcel?

Usually USPS Ground Advantage for parcels under a few pounds, bought at commercial (online) prices rather than retail counter prices — the commercial discount grows with weight and zone. Media Mail is cheaper still but restricted to books, media, and educational material and subject to inspection. Dimensional weight prices large light parcels, so the smallest box that protects the contents is the cheapest box.

Does USPS postage depend on distance?

For parcels, yes: parcels are priced by zone, the distance between origin and destination ZIP codes (zones 1–9). Letters and flats are not zoned — a letter costs the same to any US address. That is why the letter/flat boundary matters: crossing it introduces zone pricing on top of the higher flat rate.

What is a Forever stamp?

A stamp that always mails a 1 oz First-Class letter, whatever the current rate. Bought at 78¢ under the July 2025 schedule, it remains valid at that value through every future rate rise. It covers 1 oz only — additional ounces need additional postage at the current additional-ounce rate (29¢ from July 2025).

What is the difference between Priority Mail and Ground Advantage?

Speed and guarantee. Priority Mail delivers in 1–3 business days with flat-rate boxes, free boxes, and $100 included insurance; Ground Advantage delivers in 2–5 business days at a lower price, priced by weight and zone. Priority Mail Express is the overnight guaranteed service. The July 2025 rises were 6.3% for Priority Mail and 7.1% for Ground Advantage; Express was unchanged.