The edge crush test measures how much compression force a corrugated board withstands on its edge before it collapses, reported in pounds per linear inch. A small sample is stood on end between two platens and loaded until failure. ECT predicts stacking strength, so it is the figure that decides whether boxes at the bottom of a pallet hold up.
Questions or ready for a quote? Contact Teal Packaging at info@tealpackaging.com or (224) 546-8325.
Edge Crush Test: What ECT Ratings Actually Mean from Teal Packaging: 50-unit standard MOQ (100+ units for specialty rigid boxes), 2-5 business day delivery in the US (express and economy options available), free design help included on every order, free generic sample kit ($19.99 shipping, credited toward your first order). Standard production runs from about 7 business days after digital proof approval; complex or high-volume orders take longer.
Materials and certifications: FSC-certified paper stock, soy-based inks, kraft / corrugated / rigid paperboard / mylar / tin / vinyl substrates.
Contact Teal Packaging: Call (224) 546-8325, email info@tealpackaging.com, or request a free quote at tealpackaging.com/contact-us. We reply within one business day.
Updated August 25, 2026 · Teal Packaging operates a US facility in West Chicago, Illinois.
What the test actually does
A rectangular coupon is cut from a finished sheet of combined board with the flutes running vertically. It goes into a compression tester, standing on its edge, and two flat platens close on it at a controlled rate until the board buckles. The peak force divided by the specimen width gives the result in pounds per linear inch. A board rated 32 ECT carried 32 pounds for every inch of its edge before giving way.
Flute direction is the whole point. Corrugated is enormously stronger along the flutes than across them, because each wave acts as a tiny column. Load a box from above and the vertical flutes in its side walls carry that weight. Load it from the side and it folds. Everything ECT predicts assumes the box is stacked the way it was designed to stack.
Board grades and what they are rated to carry
| ECT (single wall) | Mullen equivalent | Max gross weight | Max sum of L+W+D |
|---|---|---|---|
| 23 ECT | 125 lb | 20 lb | 40 in |
| 26 ECT | 150 lb | 35 lb | 50 in |
| 29 ECT | 175 lb | 50 lb | 60 in |
| 32 ECT | 200 lb | 65 lb | 75 in |
| 40 ECT | 250 lb | 95 lb | 85 in |
| 44 ECT | 275 lb | 120 lb | 95 in |
| 55 ECT | 350 lb | 120 lb | 105 in |
Those pairings come from the published carrier board grade tables that freight classification rules have used for decades, and they are printed inside the box maker certificate stamped on the bottom flap of most shipping cartons. Carrier rules change, so confirm the current limits with your carrier rather than treating the table as permanent. The Mullen column is an equivalence for rating purposes and not a conversion; the two tests measure different things.
ECT against Mullen burst
Mullen tests puncture resistance. A rubber diaphragm pushes through the board face until it ruptures, and the result is reported in pounds per square inch. It answers a different question: can something poke through the wall, or will the box survive rough handling and impact. ECT answers whether the box holds weight from above.
Most retail and ecommerce freight is a stacking problem, so ECT has become the default specification. Loads that are dense, sharp or handled roughly still favor a Mullen specification. A board can rate well on one test and unremarkably on the other, since burst strength depends heavily on liner quality while edge crush depends on the combined structure of liners plus medium.
Why the rating is optimistic
Test conditions are controlled: conditioned board, fresh sample, load applied straight down over a few seconds. Real pallets are none of those. Moisture is the largest factor, and board sitting in a humid warehouse or a container crossing the tropics loses a meaningful share of its compression strength. Time matters too, since board under constant load creeps and slowly deforms rather than failing suddenly.
Anything cut into the wall reduces it further. Hand holes, ventilation slots and display perforations all interrupt the vertical columns doing the work. Misaligned stacking is just as costly, because strength concentrates at the corners and a box overhanging its pallet loses the support exactly where it is strongest.
Practical response: choose a grade with headroom above the calculated load rather than one that matches it exactly, and test a packed sample if the stack will be high or the storage will be humid.
Flute choice sits alongside the rating
Two boards can share an ECT figure while behaving quite differently. Flute profile governs thickness, cushioning and print quality, and the same rating can be reached with different combinations of liner and medium. A thicker profile gives more cushioning for the same crush number, while a finer profile gives a smoother surface for graphics. The tradeoffs are laid out where we put B flute against E flute, and in the full corrugated flute types reference.
Specifying a grade on a Teal quote
Give us the packed weight of one unit, how many units stack on a pallet, how high they stack, and where the pallet sits before it ships. Those four answers determine the grade far better than a number copied from a previous supplier. Retail packaging that travels inside a master carton often needs less board than buyers assume, because the outer carton carries the load. Ecommerce packaging shipped as a single parcel needs enough to survive a conveyor and a delivery van rather than a warehouse stack.
Corrugated structures are quoted under custom boxes, and printed shipping formats sit at mailer boxes. Ask for a sample of the proposed grade before a large run; feeling the board settles arguments that a specification sheet cannot. Eligible runs begin at a 50 piece minimum.
