40 ECT B flute: box compression and stacking table

40 ECT B flute pairs a 40 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 575 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 B flute
Inside size, in	0 days	10 days	30 days	90 days	180 days
8 × 6 × 4	439	277	264	242	220
10 × 8 × 6	498	314	299	274	249
12 × 12 × 12	575	362	345	316	288
14 × 10 × 8	575	362	345	316	288
16 × 12 × 10	621	391	373	342	311
18 × 12 × 12	643	405	386	354	322
18 × 18 × 18	704	444	423	387	352
20 × 16 × 14	704	444	423	387	352
24 × 18 × 18	761	479	457	418	380
24 × 24 × 24	813	512	488	447	407

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 ≈ 551 lbf
Gross weight per box	10 lb	20 lb	30 lb	40 lb	60 lb
Boxes high	34	17	12	9	6

16 × 12 × 10 in, BCT ≈ 621 lbf
Gross weight per box	10 lb	20 lb	30 lb	40 lb	60 lb
Boxes high	38	19	13	10	7

20 × 16 × 12 in, BCT ≈ 704 lbf
Gross weight per box	10 lb	20 lb	30 lb	40 lb	60 lb
Boxes high	43	22	15	11	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.