About DimMath
Nobody talks about the moment a shipment costs more than you expected.
You priced the product. You calculated the fees. You hit ship. Then the charge came through and the margin you planned for was gone. Not because you made a bad decision. Because the number you used was wrong before you even started.
DIM weight charges catch part-time sellers the most. You ship a light item in a big box and the carrier bills you for the volumetric weight, not the actual weight. The difference can double your shipping cost on a single order. Most sellers find out after the fact.
FBA sellers run into the same wall differently. The product looks profitable on paper. Then referral fees, fulfillment fees, inbound shipping, and COGS stack up and the margin disappears. There is no free tool that puts all of that in one place and just tells you: GO or NO-GO before you order inventory.
DimMath was built to close that gap.
Enter your dimensions and weight. See all four carriers side by side: UPS Ground, FedEx Ground, USPS Ground Advantage, USPS Cubic. Cheapest option highlighted. If a rate applies to your package, you see it. If it doesn't and why, you see that too.
Some tools (box fit, cubic eligibility, FBA fee math) run in the browser. DIM Weight and Carrier Savings also call DimMath's /api/shipping-compare estimate service. Those results are not live carrier quotes. Official carrier and agency pages listed on the homepage are references for checking estimates. They do not prove every displayed number was audited on a schedule. Logged changes appear in the public changelog. Not every changelog line cites a source document.
No login. No subscription. Just the answer before the box is sealed.
What DimMath Is Not
DimMath does not quote live shipping rates.
Real shipping costs depend on your negotiated carrier rates, weekly fuel surcharges that change every Monday, residential delivery fees, account-specific pricing, and surcharges that vary by package and destination. No calculator can replicate that accurately without direct API access to your carrier account.
DimMath gives you the billable weight, the duty estimate, and the fee framework. For live rate quotes with your actual carrier contract pricing use the carrier's official rate calculator or your shipping platform's label purchase screen.
Operational Integrity
Rate tables used by the estimate API and calculators live in DimMath's database. Updates are logged in the Changelog when we record them, and downloadable snapshots are published on our Open Rate Data page. There is no demonstrated automatic stale-data detector and no claimed fixed review calendar.
Disclaimers
Rates are retail estimates and may not reflect negotiated discounts or peak surcharges. DimMath is not affiliated with UPS, FedEx, USPS, DHL, or Amazon.