Edge Crush Test (ECT) Calculator and Chart

Find the minimum corrugated board rating for a shipping box. Enter the packed weight and outside size, and the calculator reads the published ECT and burst (Mullen) table: for example, 32 ECT single wall is rated for up to 65 lb and 75 in (length + width + depth).

ECT calculator

Enter the packed weight (box plus everything inside) and the box's outside size. Nothing is sent anywhere: it runs in your browser.

Packed weight (lb) Length (in) Width (in) Depth (in)

Minimums from the published table below. Add a margin for stacking, humidity, long storage or fragile goods, and confirm with your carrier and box maker.

How to read the ECT chart

Each row is a minimum for a box of that wall type: the heaviest the box and its contents together may weigh, and the largest its outside length, width and depth may add up to. A box qualifies by either its edge crush test (ECT) rating or its burst (Mullen) rating. The two columns are alternatives, not a conversion: ECT measures stacking strength (board crushed on its edge), burst measures resistance to puncture. Pick the first row where both your weight and your size sum fit.

Example: a shipping box 12 x 10 x 6 in (sum 28 in) packed at 15 lb fits the first single-wall row (up to 20 lb and 40 in), so the minimum is 23 ECT; many shippers still choose 32 ECT, the common single-wall grade for everyday shipping boxes, for extra stacking margin. A 30 lb box 20 x 16 x 14 in (sum 50 in) needs at least 26 ECT; a 70 lb box needs 40 ECT single wall or a double-wall board.

Single wall corrugated

Max weight of box and contents	Max outside dimensions (L+W+D)	Minimum ECT	Or minimum burst (Mullen)
20 lb	40 in	23 ECT	125 lb
35 lb	50 in	26 ECT	150 lb
50 lb	60 in	29 ECT	175 lb
65 lb	75 in	32 ECT	200 lb
80 lb	85 in	40 ECT	250 lb
95 lb	95 in	44 ECT	275 lb
120 lb	105 in	55 ECT	350 lb

Double wall corrugated

Max weight of box and contents	Max outside dimensions (L+W+D)	Minimum ECT	Or minimum burst (Mullen)
100 lb	95 in	48 ECT	275 lb
120 lb	105 in	51 ECT	350 lb
140 lb	110 in	61 ECT	400 lb
160 lb	115 in	71 ECT	500 lb
180 lb	120 in	82 ECT	600 lb

Triple wall corrugated

Max weight of box and contents	Max outside dimensions (L+W+D)	Minimum ECT	Or minimum burst (Mullen)
240 lb	110 in	67 ECT	700 lb
260 lb	115 in	80 ECT	900 lb
280 lb	120 in	90 ECT	1100 lb
300 lb	125 in	112 ECT	1300 lb

What the chart does not cover

It is a minimum, not a design. The rows come from the freight classification rules for fiberboard boxes (NMFC Item 222), which set minimum board grades by weight and size. They do not account for long warehouse storage, damp conditions, heavy stacking on pallets or fragile contents, all of which call for stronger board or inserts.
Parcel carriers set their own packing guidance for UPS, FedEx, USPS and Canada Post shipments; check theirs for heavy or high-value parcels.
The box maker's certificate (the round stamp on a bottom flap) shows which test a box was made to and its rating, size limit and gross weight limit.
Mailer boxes for light e-commerce orders are usually E-flute or B-flute single wall; ask for the ECT when you order.

Sources

Chart rows copied from the strength equivalency charts in the first source and checked on 19 Oct 2026. If you cite this chart, please link to this page.

What ECT rating do I need for a 50 lb box?

By the published single-wall table, a box and contents up to 50 lb with outside dimensions adding up to 60 in or less needs at least 29 ECT (or 175 lb burst). Many shippers use 32 ECT, rated to 65 lb and 75 in, for extra margin.

How much weight can a 32 ECT box hold?

In the table, 32 ECT single wall (or 200 lb burst) is rated for a box and contents up to 65 lb with outside length, width and depth adding up to 75 in or less.

What is the difference between ECT and Mullen (burst) test?

ECT measures how much force the board takes on its edge, which predicts stacking strength. The Mullen test measures the force needed to burst through the face of the board, which relates to rough handling. A box is certified to one or the other.

Is 44 ECT single wall stronger than double wall?

Not always. 44 ECT single wall is rated to 95 lb and 95 in; the lightest double-wall row, 48 ECT, is rated to 100 lb and 95 in. Double wall adds puncture resistance and rigidity, which matters for heavy or awkward loads.

Where is the ECT rating printed on a box?

On the box maker's certificate, a round stamp usually on a bottom flap. It names the test (edge crush or bursting), the rating, the size limit and the gross weight limit.