Shipping cost comparison tool
Compare USPS, UPS, and FedEx shipping costs side by side — with dimensional weight calculated automatically from your package dimensions.
Enter weight, dimensions, and destination zone. The tool applies each carrier's DIM weight rules and shows estimated costs across four services, with the cheapest option highlighted. Flat Rate alternatives are shown when your package fits.
Shipping cost comparison inputs and results
How dimensional weight works
Dimensional (DIM) weight is a pricing method that charges for the space a package occupies rather than its actual weight when volume implies more space than weight alone would suggest. The formula is: DIM weight = (length × width × height) ÷ DIM divisor, rounded up to the next whole pound. The billable weight is whichever is higher — actual weight or DIM weight.
UPS and FedEx apply DIM weight to every package using a divisor of 139 (for inch measurements). USPS applies DIM weight only to packages larger than 1 cubic foot (1,728 cubic inches) for Priority Mail, using a divisor of 166. USPS Ground Advantage does not apply dimensional weight, making it often the best option for light, bulky packages going short distances.
USPS Flat Rate boxes bypass weight and zone entirely — any weight, any zone, one fixed price. They are most cost-effective when shipping heavy, dense items across long distances, or when the flat rate price beats the weight-based rate at your specific weight and zone combination.
About this tool
Enter your package's actual weight, dimensions (length × width × height in inches), and USPS destination zone. The tool calculates dimensional weight for each carrier — since a light but bulky package bills at a higher rate than its actual weight — and shows estimated costs across USPS Ground Advantage, USPS Priority Mail, UPS Ground, and FedEx Home Delivery. Flat Rate box options are shown when your dimensions fit. Rates are approximate 2025 retail; negotiated account rates and fuel surcharges will differ.
Frequently asked questions
What is dimensional weight and why does it matter?
Dimensional weight (DIM weight) is a calculated weight based on your package's volume rather than its actual weight. A box of pillows takes up far more truck space than a small dense package of the same weight, so carriers charge based on the space it occupies. DIM weight = (length × width × height) ÷ DIM divisor. For UPS and FedEx the divisor is 139 (inches); for USPS Priority Mail the divisor is 166, and DIM weight only applies to packages over 1 cubic foot (1,728 cubic inches). The billable weight is always whichever is higher — actual or DIM.
How do I find my USPS zone?
USPS zones depend on the distance between your origin ZIP and the destination ZIP — Zone 1 is local, Zone 8 is across the country. Look up your exact zone on the USPS website using your origin ZIP and the destination ZIP. If you ship from a single location, your most common zones will become familiar quickly.
Why are the rates different from what I see in my carrier account?
Rates shown are approximate 2025 retail (counter) rates for comparison only. Your actual rates will differ based on negotiated volume discounts, current fuel surcharges (updated weekly by UPS and FedEx, typically 15–25%), residential versus commercial delivery, additional services (signature, insurance, Saturday delivery), and package type (irregular, oversized). Commercial shipper rates from Pirateship, Shippo, or a direct carrier account are typically 30–50% below retail.
When does USPS apply dimensional weight?
USPS applies dimensional weight only to packages larger than 1 cubic foot (1,728 cubic inches) for Priority Mail and Priority Mail Express. USPS Ground Advantage does not apply dimensional weight to standard packages regardless of size. UPS and FedEx apply dimensional weight to all packages.
When are USPS Flat Rate boxes the best option?
Flat Rate boxes make sense when your package is heavy relative to its size — dense items like books, hardware, or canned goods that otherwise bill at a high weight-based rate. The Medium Flat Rate box at $17.10 can hold up to 70 lbs, so a 10-lb package going to Zone 8 is almost always cheaper via Flat Rate than weight-based Priority Mail. For light packages, weight-based USPS Ground Advantage is typically cheaper.