How to read a box maker's certificate

Reading it line by line

The ring carries the name and city of the company that made the box. Inside the ring, the certificate says whether the box is single, double or triple wall, and gives one of two ratings. A burst-rated box shows its bursting test, such as 200 lb per square inch, and the minimum combined weight of its facings, the liners. An ECT-rated box shows its edge crush test, such as 32 ECT, in pounds per inch.¹²

Below the rating, two limits: the size limit, which is the largest sum of the box's length, width and depth that the rating covers; and the gross weight limit, the most the packed box should weigh. For single wall at 32 ECT or 200#, that gross weight figure is 65 lb.

Why carriers care

Motor freight classification rules have long set packaging requirements by referring to the certificate. A claim for damaged goods can turn on whether the box was rated for what was in it. The NMFTA, which publishes the freight classification, describes the certificate as information too many shippers overlook.¹ If a box is overweight for its stamp, the shipper carries the risk.

Using it when you buy

The certificate is the shortest way to tell a supplier what you use now. Turn over one of your current boxes, read the stamp, and put its rating on the quote with the inside size. If the stamp says 32 ECT and your packed box weighs 70 lb, you have found why boxes are failing. If it says 275# double wall and your box weighs 20 lb, you may be paying for board you do not need.

A box with no stamp is not rated. That is fine for some uses, such as inner cartons and storage, but a shipper relying on a rating should ask for certified board.

What the stamp does not say

It does not give the flute, the box style or the inside size. It does not tell you how the box will perform after weeks in a damp warehouse. And it applies to the box as made; a box cut down, re-taped or reused is no longer the box the certificate describes.

Glossary of the stamp

Bursting test: pounds per square inch to rupture the board. Edge crush: pounds per lineal inch the edge withstands. Minimum combined weight of facings: liner paper in pounds per thousand square feet. Size limit: maximum outside length plus width plus depth, in inches. Gross weight limit: heaviest allowed packed box, in pounds. Certifying company: the maker’s name, city and state, printed around the ring.

Checking a delivery against its stamp

When boxes arrive, check a few bundles: does the stamp match what was ordered, single or double wall, ECT or burst, and the expected figure? Is it printed clearly on every box? Keep one sample from each delivery, labelled with the date, so that if a later batch behaves differently you have something to compare. Plants record their production; a matching sample makes any conversation about quality quicker and fairer.

When a box has no certificate

Unrated boxes are common for inner packs, retail cartons, storage boxes and products that never travel by common carrier. Some economy boxes from catalogue sellers are also unrated. They are not necessarily weak, but there is no stated limit to rely on. If a carrier, insurer or customer asks what your box is rated to, an unrated box has no answer. For shipping goods by freight or parcel, we quote rated board.

Certificates also appear on bulk boxes, where the gross weight limits are higher and the size limits larger. Read them the same way.

Rated boxes and parcel carriers

Parcel carriers publish their own packaging guidelines and generally expect a sturdy box suited to the contents. Some guidance refers to burst or ECT ratings for given weights. Following the certificate limits is a reasonable baseline; heavy, fragile or high-value items deserve more.

For freight shipments, motor carriers' tariff rules and the National Motor Freight Classification have referred to box construction for decades.

History of the stamp

The certificate dates from the early days of shipping in corrugated, when railroads and later truck carriers set packaging rules so that damage claims could be judged fairly. The rules named the construction a box needed for a given weight and size, and the stamp proved the box met them. Over time edge crush ratings were added alongside the older burst ratings, and today a shipper can choose either.

The stamp is sometimes called the box certificate, the BMC or simply the test stamp. Printed in a single colour, often on the bottom flap where it is out of the way, it is easy to overlook until a claim depends on it.

An example

Imagine a single wall RSC whose certificate reads 32 ECT and gross weight limit 65 lb. Packed with 40 lb of books, it is within its rating. Packed with 80 lb of fasteners, it is not, and a damaged load would be hard to claim. The same box in 48 ECT double wall would carry up to 100 lb. A minute with the scale and the stamp avoids a costly mistake.

Certificates on our quotes

When we quote a rated box, we state the rating it will carry on its certificate. If you need a particular rating because a carrier, a customer or your own process requires it, put it on the request; we quote to that rating and no lower.