40 ECT C flute: box compression and stacking table

40 ECT C flute pairs a 40 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 643 lbf of top-to-bottom compression before any allowance for storage or humidity.

Compression, derated for storage time

BCT after storage losses, lbf, 40 ECT C flute
Inside size, in	0 days	10 days	30 days	90 days	180 days
8 × 6 × 4	491	309	295	270	246
10 × 8 × 6	557	351	334	306	278
12 × 12 × 12	643	405	386	354	322
14 × 10 × 8	643	405	386	354	322
16 × 12 × 10	695	438	417	382	347
18 × 12 × 12	719	453	431	395	359
18 × 18 × 18	788	496	473	433	394
20 × 16 × 14	788	496	473	433	394
24 × 18 × 18	851	536	510	468	425
24 × 24 × 24	909	573	546	500	455

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 ≈ 616 lbf
Gross weight per box	10 lb	20 lb	30 lb	40 lb	60 lb
Boxes high	37	19	13	10	7

16 × 12 × 10 in, BCT ≈ 695 lbf
Gross weight per box	10 lb	20 lb	30 lb	40 lb	60 lb
Boxes high	42	21	14	11	7

20 × 16 × 12 in, BCT ≈ 788 lbf
Gross weight per box	10 lb	20 lb	30 lb	40 lb	60 lb
Boxes high	48	24	16	12	8

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
32 ECT	-8 lb/in	-20%
44 ECT	+4 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.