42 ECT board: what it holds

42 ECT board carries 42 lb per inch of edge in an edge crush test. Built into a 12 × 12 × 12 in BC double wall box, the simplified McKee formula puts its compression strength near 906 lbf.

Estimated box compression by flute

Simplified McKee BCT, lbf, empty box
Inside size, in	BC double wall	EB double wall
8 × 6 × 4	692	565
10 × 8 × 6	785	641
12 × 12 × 12	906	740
14 × 10 × 8	906	740
16 × 12 × 10	979	799
18 × 12 × 12	1,013	827
18 × 18 × 18	1,110	906
20 × 16 × 14	1,110	906
24 × 18 × 18	1,198	978
24 × 24 × 24	1,281	1,046

Working load after storage

McKee gives the strength of a new, dry box. In storage it loses strength. Using Packgent's default storage losses (an assumption, see method), this is the most the bottom BC double wall box can carry at each age:

Allowed load on the bottom box, lbf (BC double wall, 42 ECT)
Inside size, in	0 days	10 days	30 days	90 days	180 days
8 × 6	692	436	415	381	346
10 × 8	785	494	471	432	392
12 × 12	906	571	544	498	453
14 × 10	906	571	544	498	453
16 × 12	979	616	587	538	489
18 × 12	1,013	638	608	557	506

Neighbouring grades

Grade	ECT change	BCT change, same flute and size
48 ECT	+6 lb/in	+14%

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.