Shipping Cost Optimizer

Dimensional weight approximates how much cargo space a package occupies: length times width times height, divided by a DIM divisor (139 in this calculator). Carriers bill on the greater of actual weight or dimensional weight, so a large, lightly-packed box can cost more to ship than a small, dense one of the same actual weight — the carrier is pricing the space it takes on the truck or plane, not just the scale reading. The 139 divisor is now the common figure across carriers for standard service: USPS moved from 166 to 139 on 12 July 2026 to match UPS and FedEx, which raised dimensional weight on affected USPS packages by roughly 19%. The one surviving 166 divisor is UPS Retail Rates (walk-in counter pricing), an account-type distinction this calculator does not model.

Each carrier's rate is a base fee plus a per-pound charge on billable weight, and the per-pound rate differs by carrier — USPS's marginal per-pound cost is higher here than UPS's or FedEx's, even though its base fee is lower. That makes USPS cheapest for small, light packages and lets UPS or FedEx pull ahead as billable weight climbs, so the cheapest option at 2 pounds is not guaranteed to stay cheapest at 50 pounds.

Zone adds a flat per-zone increment to each carrier's base rate — for example, moving from zone 1 to zone 9 adds several dollars, scaled by each carrier's own per-zone rate. It's a smaller swing than a large jump in package weight, but it applies on every shipment regardless of size, so it still matters for high-volume shippers comparing carriers.

This calculator applies a simplified volume discount that ramps in continuously: no discount at or below 200 shipments a month, growing steadily to a 10% reduction at 1,000 a month and holding there. Real carrier account pricing is negotiated case by case, is often structured in banded tiers rather than a smooth ramp, and can differ substantially from this simplified model.

No — these are simplified estimates built to let you compare the three carriers' relative pricing behavior, not a quote from any carrier's real, currently-published rate card. Actual invoiced cost also depends on package type, fuel surcharges, residential or signature-required fees, and any negotiated account discount, none of which this estimate includes.