29 ECT C flute: box compression and stacking table

29 ECT C flute pairs a 29 lb/in edge crush with a nominal 0.156 in caliper. As an empty 12 × 12 × 12 in box, the simplified McKee formula puts it near 466 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 C flute
Inside size, in	0 days	10 days	30 days	90 days	180 days
8 × 6 × 4	356	224	214	196	178
10 × 8 × 6	404	254	242	222	202
12 × 12 × 12	466	294	280	256	233
14 × 10 × 8	466	294	280	256	233
16 × 12 × 10	504	317	302	277	252
18 × 12 × 12	521	328	313	287	261
18 × 18 × 18	571	360	343	314	285
20 × 16 × 14	571	360	343	314	285
24 × 18 × 18	617	389	370	339	308
24 × 24 × 24	659	415	396	363	330

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 ≈ 446 lbf
Gross weight per box	10 lb	20 lb	30 lb	40 lb	60 lb
Boxes high	27	14	9	7	5

16 × 12 × 10 in, BCT ≈ 504 lbf
Gross weight per box	10 lb	20 lb	30 lb	40 lb	60 lb
Boxes high	31	16	11	8	6

20 × 16 × 12 in, BCT ≈ 571 lbf
Gross weight per box	10 lb	20 lb	30 lb	40 lb	60 lb
Boxes high	35	18	12	9	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.