Side-by-side dimensional weight comparison. Same package, two carriers — see exactly what each would bill, and which wins for your shipment profile.
Awaiting dimensions. Enter package details to compute billable weight.
USPS has the more favorable divisor (6000 vs 5000 cm³/kg) — meaning lower billable weight for the same package.
| Royal Mail | USPS | |
|---|---|---|
| Imperial divisor (in³/lb) | Metric only | 166 |
| Metric divisor (cm³/kg) | 5000 | 6000 |
| DIM applies | No minimum | 1,728 in³ (1 ft³) |
| Region | United Kingdom | United States |
UK-origin international parcels, EU and Commonwealth destinations
Small or heavy dense packages, Flat Rate boxes, light-volume shippers
Divisors don't tell you everything — base rates, fuel surcharges, and discounts also matter.
Royal Mail ↗
USPS ↗
It depends on your package. Royal Mail's divisor is 5000 cm³/kg, while USPS's is 6000 cm³/kg. For DIM-weighted packages (lightweight bulky), the carrier with the higher divisor wins on billable weight. For dense packages where actual weight wins, the divisor doesn't matter and the cheaper base rate wins. Use the calculator above to see which gives you the lower billable weight for your specific package.
The formula is the same: volume divided by the divisor, rounded up, with the billable weight being the greater of the result or the actual weight. The divisors differ (5000 cm³/kg for Royal Mail, 6000 cm³/kg for USPS), which is what produces different billable weights for the same package.
Yes — many shippers use both, routing each package to whichever carrier is cheaper for that shipment profile. Multi-carrier rate-shopping platforms (Shippo, ShipStation, Easyship) automate this decision in real time based on weight, dimensions, destination, and your negotiated rates with each carrier.
This page focuses on Royal Mail vs USPS. To see how all major carriers compare for your specific shipment, use the main calculator with the global setting.
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