55 ECT E flute: box compression and stacking table

55 ECT E flute pairs a 55 lb/in edge crush with a nominal 0.063 in caliper. As an empty 12 × 12 × 12 in box, the simplified McKee formula puts it near 559 lbf of top-to-bottom compression before any allowance for storage or humidity.

Compression, derated for storage time

BCT after storage losses, lbf, 55 ECT E flute
Inside size, in	0 days	10 days	30 days	90 days	180 days
8 × 6 × 4	427	269	256	235	214
10 × 8 × 6	484	305	291	266	242
12 × 12 × 12	559	352	336	308	280
14 × 10 × 8	559	352	336	308	280
16 × 12 × 10	604	381	362	332	302
18 × 12 × 12	625	394	375	344	313
18 × 18 × 18	685	431	411	377	342
20 × 16 × 14	685	431	411	377	342
24 × 18 × 18	740	466	444	407	370
24 × 24 × 24	791	498	474	435	395

0 days is the McKee estimate itself. Storage losses are Packgent's default assumptions (10 days 37%, 30 days 40%, 90 days 45%, 180 days 50%), not sourced values; edit them in the stacking calculator.

How many high can it stack?

Boxes high, including the bottom one, column stacked for 30 days, before humidity, interlock or overhang losses.

12 × 10 × 8 in, BCT ≈ 535 lbf
Gross weight per box	10 lb	20 lb	30 lb	40 lb	60 lb
Boxes high	33	17	11	9	6

16 × 12 × 10 in, BCT ≈ 604 lbf
Gross weight per box	10 lb	20 lb	30 lb	40 lb	60 lb
Boxes high	37	19	13	10	7

20 × 16 × 12 in, BCT ≈ 685 lbf
Gross weight per box	10 lb	20 lb	30 lb	40 lb	60 lb
Boxes high	42	21	14	11	7

Boxes high = ⌊BCT × (1 − 0.4) ÷ gross weight⌋ + 1. A real stack needs further allowance for humidity, pattern and handling.

Neighbouring grades

Grade	ECT change	BCT change, same flute and size
48 ECT	-7 lb/in	-13%

In McKee, BCT scales directly with ECT, so the percentage change in strength equals the change in ECT.

Freight rule limits

NMFC Item 222 ties each grade to a maximum gross weight and size for LTL shipping. Packgent has not published those limits yet because they could not be checked against the current tariff. See the Item 222 page for status.

Sources

TAPPI T 811: Edgewise compressive strength of corrugated fibreboard (short column test)
McKee, R.C., Gander, J.W. & Wachuta, J.R. (1963). "Compression strength formula for corrugated boxes." Paperboard Packaging 48(8): 149–159
Flute calipers: Foster (1997), Wiley Encyclopedia of Packaging Technology

Last reviewed 2026-10-27. See all sources and how Packgent computes.