Updated July 2, 2026
What determines a shipping rate?
Carrier rates for the same package can differ by 30 percent or more, and the gap comes from four inputs: weight, package size (dimensional weight), distance (zone), and speed. The Shipping Rate Estimator compares modeled rates side by side so you can see the likely cheapest option for a given package and destination. For most parcels, the cost surprise comes from size, not weight - a shoebox of foam peanuts will teach you this faster than any guide.
Dimensional weight
Carriers bill the greater of actual weight and dimensional (DIM) weight, which converts a package's volume into a billable weight. A big, light box can cost far more than its scale weight suggests. The Dimensional Weight calculator shows the DIM weight before you ship. USPS is changing its own DIM divisor from 166 to 139 on July 12, 2026 (see the DIM weight guide for the source), which will make USPS pricing behave more like UPS and FedEx on oversized boxes.
Zones and speed
Shipping zones measure distance from origin to destination; higher zones cost more. Speed multiplies that cost, since overnight and two-day rates run far above ground. Choosing ground when timing allows, and shipping from a location closer to customers, both cut zone-driven charges.
How carriers differ
USPS often wins on small, light packages; UPS and FedEx are competitive for heavier or larger parcels and offer deeper business discounts. Regional carriers can beat all three on certain lanes. No carrier wins every shipment, so comparing per package is where the actual savings are; see the modeled tiers on the 2026 cost comparison reference.
Ways to cut cost
Right-size packaging to reduce DIM weight, compare carriers per shipment, use flat-rate options for dense items, negotiate volume discounts, and buy postage online rather than at the counter. Consolidating shipments and placing inventory closer to the customer both reduce zone charges.
All calculators on this site
- Shipping Rate Estimator - modeled USPS, UPS & FedEx rates side by side.
- Dimensional Weight - billable (DIM) weight for any package.
Run your package through the model
See where your own package lands once weight, size, and zone are all in the mix.