29 ECT B flute: box compression and stacking table

29 ECT B flute pairs a 29 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 417 lbf of top-to-bottom compression before any allowance for storage or humidity.

Compression, derated for storage time

BCT after storage losses, lbf, 29 ECT B flute
Inside size, in	0 days	10 days	30 days	90 days	180 days
8 × 6 × 4	318	201	191	175	159
10 × 8 × 6	361	228	217	199	181
12 × 12 × 12	417	263	250	229	208
14 × 10 × 8	417	263	250	229	208
16 × 12 × 10	450	284	270	248	225
18 × 12 × 12	466	294	280	256	233
18 × 18 × 18	511	322	306	281	255
20 × 16 × 14	511	322	306	281	255
24 × 18 × 18	552	348	331	303	276
24 × 24 × 24	590	372	354	324	295

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 ≈ 399 lbf
Gross weight per box	10 lb	20 lb	30 lb	40 lb	60 lb
Boxes high	24	12	8	6	4

16 × 12 × 10 in, BCT ≈ 450 lbf
Gross weight per box	10 lb	20 lb	30 lb	40 lb	60 lb
Boxes high	28	14	10	7	5

20 × 16 × 12 in, BCT ≈ 511 lbf
Gross weight per box	10 lb	20 lb	30 lb	40 lb	60 lb
Boxes high	31	16	11	8	6

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
26 ECT	-3 lb/in	-10%
32 ECT	+3 lb/in	+10%

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.