Resource Guide

Box Grades Guide

This guide covers flute types, wall constructions, strength ratings, the box maker certificate stamped on many boxes, and the condition grades commonly used for used boxes.

Flute Types

The flute is the wavy layer between the flat liners. The letters reflect the order in which the profiles were developed, not their quality.

Flute	Relative Thickness	Strengths	Common Uses
A-flute	Thickest	Cushioning, stacking	Fragile items
B-flute	Thin	Flat crush resistance, printing	Canned goods, displays
C-flute	Medium	All-round performance	General shipping boxes
E-flute	Very thin	Smooth print surface, slim profile	Mailers, retail packaging
F-flute	Thinnest	Fine printing	Retail and specialty packaging

Wall Types

Single Wall

One fluted layer between two liners. The most common construction for shipping boxes, mailers, and retail packaging.

Liner | Flute | Liner

Double Wall

Two fluted layers between three liners, often BC or AC flute. Used for heavier shipments and most gaylords.

Liner | Flute | Liner | Flute | Liner

Triple Wall

Three fluted layers between four liners, for the heaviest loads. Sometimes used in place of wooden crates.

Four liners, three flutes

ECT and Burst Ratings

The Edge Crush Test (ECT) measures how much force a strip of board can take on its edge before crushing, in pounds per linear inch. It predicts stacking strength and is now the most common rating for shipping boxes.

The Mullen burst test measures how much pressure it takes to rupture the face of the board, in pounds per square inch. It relates to puncture resistance and rough handling.

Actual box strength also depends on its dimensions, humidity, how long it is stored, and how it is stacked. Humidity in particular weakens corrugated board, so allow extra margin for damp storage or long transit.

Common Single Wall Equivalents

Approximate pairings often printed on box maker certificates.

Burst Test	ECT	Gross Weight Limit
200# test	32 ECT	65 lbs
275# test	44 ECT	95 lbs
350# test	55 ECT	120 lbs

Reading a Box Maker Certificate

Many corrugated boxes carry a round or rectangular stamp on a bottom flap called the box maker certificate (BMC). It typically shows the wall type, the burst or ECT rating, and, on burst-rated boxes, the minimum combined weight of the facings, the size limit (length + width + height), and the gross weight limit, along with the manufacturer.

For used boxes, the stamp tells you what the box was designed for. Wear, moisture, and previous use reduce strength, so treat the rating as a ceiling rather than a guarantee.

Used Box Condition Grades

Grade names vary by supplier. These are common descriptions; confirm the grade in your quote.

Grade A: Like New

Minimal use marks, flaps intact with clean edges, no moisture damage or odors, little tape residue. Suited to customer-facing shipments.

Grade B: Good

Visible signs of use such as scuffs, creases, tape residue, or labels, but structurally sound. Suited to business shipping, storage, and moving.

Grade C: Fair

Noticeable wear, writing, or dents, while still closing and sealing properly. Suited to internal use and storage.

Choosing a Grade

Product Weight

Heavier products need higher ECT ratings or double wall. Check the gross weight limit on the box certificate and test with your actual product.

Parcel Shipping

Boxes are dropped and tossed, so puncture resistance matters along with stacking strength.

Palletized Freight

Stacking is the main hazard, so ECT is the key specification.

Long or Damp Storage

Humidity weakens board over time. Allow extra strength for damp conditions or long storage.

Need the Right Grade?

Describe what you are shipping in a quote request and a partner supplier can suggest a suitable grade.

Request a Quote Size Guide Industry Standards