26 ECT B flute: box compression and stacking table

26 ECT B flute pairs a 26 lb/in edge crush with a nominal 0.125 in caliper. As an empty 12 × 12 × 12 in box, the simplified McKee formula puts it near 374 lbf of top-to-bottom compression before any allowance for storage or humidity.

Compression, derated for storage time

BCT after storage losses, lbf, 26 ECT B flute
Inside size, in	0 days	10 days	30 days	90 days	180 days
8 × 6 × 4	286	180	171	157	143
10 × 8 × 6	324	204	194	178	162
12 × 12 × 12	374	236	224	206	187
14 × 10 × 8	374	236	224	206	187
16 × 12 × 10	404	254	242	222	202
18 × 12 × 12	418	263	251	230	209
18 × 18 × 18	458	288	275	252	229
20 × 16 × 14	458	288	275	252	229
24 × 18 × 18	495	312	297	272	247
24 × 24 × 24	529	333	317	291	264

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 ≈ 358 lbf
Gross weight per box	10 lb	20 lb	30 lb	40 lb	60 lb
Boxes high	22	11	8	6	4

16 × 12 × 10 in, BCT ≈ 404 lbf
Gross weight per box	10 lb	20 lb	30 lb	40 lb	60 lb
Boxes high	25	13	9	7	5

20 × 16 × 12 in, BCT ≈ 458 lbf
Gross weight per box	10 lb	20 lb	30 lb	40 lb	60 lb
Boxes high	28	14	10	7	5

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
23 ECT	-3 lb/in	-12%
29 ECT	+3 lb/in	+12%

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.