The postal cost of an item by weight starts at $0.78 for a one-ounce First-Class letter and climbs from there, with each additional ounce adding $0.29 up to the 3.5-ounce letter limit.1United States Postal Service. USPS Notice 123 – January 2026 Price Change Once you’re mailing a package rather than a letter, weight is only half the calculation. The distance the package travels can matter as much or more, and the size of the box can override the number on your scale entirely. Knowing the weight, the destination ZIP, and the outside dimensions before you buy postage is what keeps you from overpaying.
Letter and Large Envelope Rates
First-Class Mail is the cheapest way to send anything light. A stamped letter costs $0.78 for the first ounce, $1.07 for two ounces, $1.36 for three ounces, and $1.65 at the 3.5-ounce maximum. Buying postage through a meter or online drops the one-ounce rate to $0.74, a four-cent saving per piece.1United States Postal Service. USPS Notice 123 – January 2026 Price Change
Large envelopes, called flats, can weigh up to 13 ounces and still ship as First-Class Mail. Anything heavier than 13 ounces automatically gets bumped to Priority Mail pricing.2United States Postal Service. First-Class Mail – Postal Explorer Watch this threshold. A flat at 12.9 ounces ships for a few dollars; the same flat at 13.1 ounces jumps to Priority Mail rates that start much higher.
Letters with unusual shapes face a $0.49 non-machinable surcharge, because they can’t run through USPS sorting equipment.3United States Postal Service. Notice 123 – Postal Explorer Square envelopes, rigid cards, and anything with lumpy or uneven thickness all trigger the fee. A square greeting card at one ounce ends up costing $1.27 rather than $0.78.
Package Rates by Pound and Zone
USPS Ground Advantage is the main service for packages, handling items from one ounce up to 70 pounds. Under a pound, USPS uses four weight tiers: up to 4 ounces, up to 8 ounces, up to 12 ounces, and up to 15.999 ounces. Your package rounds up to the next tier, so a 4.2-ounce item pays the 8-ounce price.4United States Postal Service. USPS Ground Advantage
Once you cross 15.999 ounces, the package rounds up to one pound and enters pound-rate pricing. From there, the price depends on both the weight and the USPS zone, which measures the distance between origin and destination ZIP codes. Some representative January 2026 retail prices show how the two variables combine:5United States Postal Service. USPS Notice 123 – Domestic Prices
- 1 lb, Zone 1 (local): $19.80
- 1 lb, Zone 5 (medium distance): $37.00
- 1 lb, Zone 8 (cross-country): $58.20
- 5 lbs, Zone 1: $24.30
- 5 lbs, Zone 5: $40.15
- 5 lbs, Zone 8: $72.70
- 10 lbs, Zone 1: $31.05
- 10 lbs, Zone 5: $55.85
- 10 lbs, Zone 8: $92.60
Look at what happens across the rows versus down them. Adding four pounds to a local one-pound shipment costs about $4.50 more. Sending that same one-pound package cross-country instead of across town costs about $38 more. Distance drives the bill harder than weight does. If you’re trying to shave costs, the destination affects your price more than trimming a few ounces off the scale.
Zones run from Zone 1 (local) up through higher numbers for greater distances, and the first three digits of the destination ZIP determine which zone applies.6United States Postal Service. Domestic Zone Chart – Retail Postage Price Calculator There is no way to opt out. If it’s going farther, it costs more.
When Flat Rate Beats Weight-Based Pricing
Priority Mail Flat Rate boxes ignore weight and distance entirely. Anything that fits inside the box ships at one fixed price up to 70 pounds, anywhere in the country. The 2026 retail prices:3United States Postal Service. Notice 123 – Postal Explorer
- Small Flat Rate Box: $12.65
- Medium Flat Rate Box: $22.95
- Large Flat Rate Box: $31.50
Flat Rate wins when the item is heavy, dense, and traveling a long way. Fifteen pounds of hardware in a Medium Flat Rate Box costs $22.95 whether it’s going next door or to Hawaii. The same 15-pound package shipped Ground Advantage to Zone 8 would run over $107. Flat Rate is a poor choice for lightweight items or short-distance shipments, where regular weight-based pricing beats it easily. Priority Mail also comes with tracking and insurance included, which weight-based Ground Advantage service does not automatically match.7United States Postal Service. Priority Mail
When Box Size Overrides the Scale
The number on your scale is not always what you pay for. USPS also calculates dimensional weight by multiplying length by width by height in inches and dividing by 139. If that dimensional weight exceeds the actual weight, you pay based on the larger figure. The rule applies to Ground Advantage, Priority Mail, and Priority Mail Express for packages that exceed one cubic foot.8United States Postal Service. Domestic Competitive Products Pricing and Mailing Standards Changes
A box of pillows might weigh three pounds on the scale but measure 24 by 18 by 16 inches. That works out to 6,912 cubic inches divided by 139, or roughly 50 pounds of dimensional weight. You would pay the 50-pound rate. The fix is straightforward: use the smallest box the contents will fit into. Measure the outside of the box, not the inside, because that is what USPS equipment reads.
What Happens If Your Weight Is Wrong
USPS does not take your word for it. Automated Package Verification re-weighs and re-measures packages as they move through processing centers, using scales calibrated daily. If the system finds your package is heavier or larger than the label says, it charges the difference directly to the online postage account you used, and the package keeps moving.9USPS.com. Automated Package Verification Program for Domestic Packages
Your postage provider, whether Click-N-Ship, Stamps.com, eBay, or another platform, sends a notice showing the adjustment. If you think the charge is wrong, you can dispute it through the USPS APV Dispute portal using the 15-digit Revenue Assurance ID from the notice along with the tracking number.9USPS.com. Automated Package Verification Program for Domestic Packages
Packages mailed with stamps at a post office counter work under the older process. An underweighed package may come back to you, or it may be delivered postage due, meaning the recipient has to pay the shortfall before they can accept it.
Getting an Exact Price Before You Ship
A precise quote takes about two minutes. You need three pieces of information: the package weight (a kitchen scale handles light items; for heavier ones, weigh yourself holding the package and subtract your own weight), the outside dimensions of the box in inches, and the destination ZIP code.
The USPS Retail Postage Price Calculator at postcalc.usps.com takes those inputs and shows prices across every USPS service side by side.10United States Postal Service. Retail Postage Price Calculator It applies the zone, the dimensional weight rule, and any current surcharges automatically. Buying postage online rather than at the counter usually costs less, because metered and online rates run below retail stamp prices and some third-party platforms add commercial discounts on top. You print the label, tape it on, and drop the package off or schedule a free pickup.