Methodology

How dimensional weight is calculated

DimCheck rounds each measured side the way the selected carrier publishes (FedEx, UPS, and USPS round every fraction up to the next whole inch; DHL Express has no published convention, so DimCheck uses nearest whole centimeter as a documented working assumption). The rounded sides are multiplied to get the volume, which is divided by the carrier's divisor — 139 for FedEx, UPS Daily, and USPS; 166 for UPS Retail and the generic industry standard; 5,000 cm³/kg for DHL Express. The result is rounded the way the carrier rounds DIM weight (up to the next whole pound, or up to the next 0.5 kg for DHL).

USPS applies DIM weight only when the rounded volume exceeds one cubic foot (1,728 in³), and caps DIM weight at the 70-lb price. FedEx applies a 40-lb minimum billable weight to packages that trigger Additional Handling–Dimension, and a 90-lb minimum to Ground unauthorized packages. UPS applies a 90-lb minimum to Large Packages. DimCheck encodes each of these as a rule with an official source and an effective date.

How billable weight is determined

Billable weight is the greater of the rounded actual weight and the DIM weight — and any applicable surcharge-triggered minimum. DimCheck shows all three inputs so you can see which one is driving the bill.

How threshold distance works

Every surcharge condition and size limit is evaluated against your package's carrier-rounded measurements. A threshold is TRIGGERED when the published condition is met, NEAR when it is within a small band (1 in for sides, 2 in for length + girth, 2 lb for weight, 5% for volume), and SAFE otherwise. DimCheck reports the exact distance to the nearest threshold, because one inch can change the surcharge outcome.

What safety allowance means

Safety allowance is a deterministic planning buffer: the allowance is added to every side and the analysis is re-run on those planning dimensions. If a planning dimension crosses a threshold your measured dimensions did not, the result is flagged AT RISK. It is a packaging-variation buffer — not a prediction of carrier measurement error, and not a probability model.

How Business Impact is calculated

Business Impact = DIM Excess × Monthly Shipments, expressed as Monthly Excess Billable Weight. DIM Excess is max(DIM weight − actual weight, 0). This is a weight-exposure metric, not a dollar-savings estimate — DimCheck does not estimate costs without verified rate data. Rows with missing shipment volume are shown as Unknown and never treated as zero; rows with explicitly zero shipments are excluded from the active ranking by default.

How Packaging Severity is calculated

Packaging Severity = DIM Penalty % = max(DIM weight − actual weight, 0) ÷ actual weight × 100. It answers "which SKU has the strongest dimensional-weight mismatch?" independent of shipment volume. It is not a void-space metric — it describes how far DIM weight exceeds actual weight, not how empty the box is.

Why results may differ from carrier invoices

• Carriers measure the package themselves and may measure differently than you do.
• Shape-based surcharges (packaging material, irregular shape, cylindrical items) cannot be determined from dimensions and weight alone and are not evaluated.
• Dollar amounts, zones, fuel surcharges, and seasonal charges are outside DimCheck's scope.
• Rules can change — the effective dates on the carrier rules page show which rule set DimCheck encodes.

How rule sources are maintained

Every rule in DimCheck carries the official URL it was verified against and the retrieval date. A weekly automated job re-fetches each official source and hashes the relevant text; if a page changes, the job only flags it for human review — it never edits rules automatically. See the carrier rules page for the current values, effective dates, and sources.