Estimate USPS shipping costs for Priority Mail, First-Class, flat rate boxes, and media mail. Compare services, delivery times, and find the cheapest shipping option.
Shipping costs eat into margins for online sellers and surprise consumers at checkout. The USPS Shipping Calculator estimates postage for all major USPS services — Priority Mail, First-Class Package, flat rate boxes, and media mail — so you can compare options and find the cheapest way to ship. Enter your package dimensions and weight, and instantly see rates across all applicable services.
USPS pricing depends on weight, dimensions (dimensional weight matters for large/light packages), distance (zone), and service level. Priority Mail reaches most destinations in 1-3 business days; First-Class Package Service handles items under 15.99 oz at the lowest cost; flat rate boxes ship at one price regardless of weight (up to 70 lb); and media mail offers the cheapest rates for books, DVDs, and educational materials.
This calculator uses USPS rate tables to estimate costs for shipping between ZIP codes. It calculates dimensional weight, identifies which services your package qualifies for, and highlights the cheapest option. For business shippers, it also estimates Commercial Base pricing available through USPS online postage services.
Use this calculator when you want to compare USPS services before checkout instead of guessing from the retail counter price. It is useful for sellers and occasional shippers who need to balance speed, box size, and rate class. It also helps you spot when flat rate, First-Class, or Media Mail is the better deal for the same package.
Dimensional Weight = (L × W × H) / 166. Billable Weight = max(Actual Weight, Dimensional Weight). Zone = distance between origin/destination ZIPs (1-9). Rate = Zone Rate Table lookup by weight and service.
Result: Priority Mail: $12.80, First-Class: N/A (over 1 lb), Flat Rate Medium: $16.10
A 3 lb package (12×10×6 in) shipping from LA to NYC (Zone 8) costs approximately $12.80 via Priority Mail. It exceeds First-Class limits (15.99 oz max). The medium flat rate box at $16.10 would only be cheaper if the package weighed more than about 5 lb.
USPS Ground Advantage consolidated several older package services into one option for packages up to 70 lb. Priority Mail remains the faster standard service with 1-3 day delivery and included insurance, while Priority Mail Express is the premium overnight-to-2-day option.
For sellers shipping regularly, Priority Mail Commercial rates offer significant savings — sometimes 30-40% below retail. The key is purchasing postage online rather than at the counter. Services like Pirate Ship provide free access to these commercial rates without monthly fees.
Flat rate boxes are the secret weapon for heavy items. A 20 lb Priority Mail package to Zone 8 costs $30-40+ by weight, but the large flat rate box ships for about $22 regardless of weight. The break-even point varies by zone and weight, but generally: if your item weighs over 5 lb AND fits in a flat rate box, compare rates carefully.
The flat rate boxes themselves are free — order them from usps.com for delivery to your door. Many sellers keep all three sizes stocked to use whenever the flat rate price beats the weight-based rate.
Since USPS applies dimensional weight pricing to eligible packages, packaging matters. An item in a 20×16×12 box has dimensional weight of 23 lb. If the item only weighs 3 lb, you are paying for 23 lb worth of shipping. Using right-sized boxes or poly mailers for flexible items can save substantial money.
For items under 1 lb: First-Class Package ($4-6). For books/media: Media Mail ($3-8). For general packages 1-5 lb: Priority Mail ($8-15). For heavy items: flat rate boxes may be cheapest. Ground Advantage replaced several services in 2023.
For large but light packages, USPS charges based on dimensional weight: (L×W×H)/166. You're billed the greater of actual or dimensional weight. A 20×20×20 inch box weighing 5 lb has dimensional weight of 48 lb, so you'd pay the 48 lb rate.
Small flat rate box: 8.625×5.375×1.625 in. Medium: 11×8.5×5.5 or 13.625×11.875×3.375 in. Large: 12×12×5.5 in. Flat rate envelope and padded envelope are also available. Weight limit is 70 lb for all flat rate options.
Zones 1-9 are based on distance between origin and destination ZIP codes. Zone 1 is local; Zone 8 is cross-country; Zone 9 is to/from territories. Higher zones cost more. Zone 1-4 is usually within your state or neighboring states.
Commercial Base (CB) rates are discounted prices available when you purchase postage through USPS.com Click-N-Ship, Stamps.com, Pirate Ship, or other approved services. CB rates are typically 10-20% less than retail counter rates.
Books, CDs, DVDs, educational materials, sound recordings, and some printed materials. You CANNOT send advertising, video games, computer drives, or general merchandise. USPS can inspect media mail and charge the difference if contents don't qualify.