Packaging & retail / Corrugate strength

Corrugate strength

Three references in one place: flute profiles with calipers and typical uses, ECT and Mullen board grades side by side, and a McKee-based estimate of box compression strength and safe stacking load.

Stacking strength estimate

McKee simplified formula. Enter the board and the box footprint to estimate compression strength, then derate it for real-world conditions.

Board ECT (lb/in)

Board caliper (in)

Box length, outside (in)

Box width, outside (in)

Environment derating

Weight per loaded case (lb)

Layers in the stack

Estimated compression strength (BCT)0 lb

Safe working load after derating0 lb

Load on the bottom case in your stack0 lb

Stack checkOK

Formula: BCT = 5.87 x ECT x sqrt(caliper x perimeter), with ECT in lb/in and dimensions in inches. It assumes a regular slotted carton, single stack, no pallet overhang, and no handholes or large cutouts. Treat it as a screening number and confirm with a physical compression test before committing to a board grade.

Flute profiles

Calipers are typical values; every mill runs slightly different.

Flute	Caliper (in)	Flutes / ft	Typical use
A	0.185	33	Cushioning, double wall combinations
B	0.097	47	Die-cut boxes, inner packs, counter displays
C	0.142	39	Standard shipping cases, the default RSC
E	0.046	90	Retail packaging, high-quality print surfaces
F	0.031	125	Small retail cartons, folding carton replacement
BC	0.250	\u2014	Doublewall for heavy or stacked product

ECT and Mullen, side by side

ECT predicts stacking performance; Mullen (burst) predicts puncture and rough-handling resistance. They are different tests, so the pairings below are common commercial equivalents, not conversions.

ECT grade	Common Mullen pairing	Max box + contents (lb)	Wall
23 ECT	125#	20	Single
26 ECT	150#	35	Single
29 ECT	175#	50	Single
32 ECT	200#	65	Single
40 ECT	250#	80	Single
44 ECT	275#	95	Single
48 ECT	275# DW	100	Double
51 ECT	350# DW	120	Double
61 ECT	400# DW	140	Double
71 ECT	500# DW	160	Double
82 ECT	600# DW	180	Double

Pick ECT when the box's job is stacking on a pallet. Pick Mullen when the box's job is surviving parcel shipping. Max weights follow the common carrier box maker's certificate limits.