Method: how Packgent computes
Packgent's numbers are engineering estimates from published formulas, sourced constants and labelled assumptions. This page lists every one.
Box compression (McKee)
Packgent uses the simplified McKee formula for regular slotted containers: BCT = 5.87 × ECT × √(t × Z), where BCT is the top-to-bottom compression strength in lbf, ECT is the board's edge crush in lb/in, t is board caliper in inches and Z = 2(L + W) is the box perimeter. Packgent uses the inside length and width for Z.
The formula was fitted to RSCs of ordinary proportions. Other styles, very tall or very flat boxes and printed or perforated boxes will differ. Calipers are the nominal values on the flutes page; real board varies by mill and crush on the corrugator.
Safety factor
Required BCT = load on the bottom box × SF. The load is (boxes high − 1) × gross weight per box. SF = 1 ÷ Π(1 − dᵢ) for each loss that applies; losses multiply because each one acts on the strength left by the others.
The default losses are Packgent's working assumptions, not values from a cited source. Every tool lets you change them.
| 0 days in storage | 0% loss |
|---|---|
| 10 days in storage | 37% loss |
| 30 days in storage | 40% loss |
| 90 days in storage | 45% loss |
| 180 days in storage | 50% loss |
| Humidity at or above 85% RH | 40% loss |
| Interlocked stacking | 45% loss |
| Overhang | 30% loss |
| Parcel shipping minimum SF | 3 |
Inside and outside dimensions
OD = ID + k × caliper, with k = 2 on length, 2 on width and 3 on depth for slotted boxes. The extra caliper on depth allows for the flaps folding over each other. Box makers set their own score allowances, so treat the result as an estimate within about one caliper.
Blank size
For slotted styles the blank length is 2L + 2W + a 1.25 in glue tab, plus one caliper per vertical score. The width is H plus the top and bottom flaps, plus one caliper per flap score. Flap lengths follow each style: half the width for an RSC, the full width for a full-overlap container, and so on, as described on each style page.
Dimensional weight
Each carrier's rule is applied as published: dimensions rounded (up or to the nearest inch), cubic inches divided by the divisor, the result rounded up to a whole pound, and the larger of that and the actual weight billed. Current divisors:
- USPS: divisor 139, from USPS Domestic Mail Manual 223 (Priority Mail prices and eligibility), section 1.4.
- FedEx: divisor 139, from FedEx: What is dimensional weight?.
Carriers not listed could not be checked against their own published page and are left out.
Pallet patterns
Cases are laid on a 48 × 40 in deck, 5.5 in tall, under a 60 in total load height. Packgent tries both case orientations and every two-zone split, keeps the highest count with no overhang, and stacks as many full layers as fit. These deck and height values are common defaults, not a standard, and you can change them in the pallet tool.