Corrugated Box ECT Ratings Explained

When you're buying corrugated boxes in bulk, you'll see a number stamped on the bottom or side of the box followed by "ECT" — something like 32 ECT or 44 ECT. Most buyers ignore it. That's a mistake. ECT rating is one of the most important specs for determining whether a box will actually protect your products in transit.

Here's what ECT means, how it works, and how to choose the right rating for your shipping needs.

What Is ECT?

ECT stands for Edge Crush Test. It measures how much top-to-bottom stacking pressure a corrugated box can withstand before the walls buckle. The number represents pounds of force per linear inch (lb/in). So a 32 ECT box can withstand 32 pounds of crushing force per inch along its edges before failing.

ECT replaced the older Mullen Burst Test as the dominant industry standard because it better reflects real-world shipping conditions — specifically, how boxes are stacked on pallets and in delivery trucks.

Common ECT Ratings and What They're Used For

• 23 ECT — Light-duty. Single-wall construction. Good for retail display boxes or very light products shipped individually.
• 32 ECT — Standard. The most common rating for e-commerce shipping. Handles most consumer goods up to about 65 lbs.
• 44 ECT — Heavy-duty. Single-wall construction with thicker fluting. Used for heavier products, industrial parts, or items that will be stacked in transit.
• 48 ECT — Double-wall construction. For very heavy or fragile items requiring extra rigidity and stacking strength.
• 51 ECT and above — Industrial and freight applications. Palletized shipments, heavy equipment, bulk wholesale orders.

ECT vs. Burst Strength: What's the Difference?

You may also see boxes rated by burst strength (measured in PSI), which tests how much pressure the box wall can withstand before puncturing. Burst strength is more relevant for boxes that will be handled roughly or exposed to sharp objects. ECT is more relevant for stacking and compression during shipping.

For most e-commerce applications, ECT is the more useful spec. If you're shipping fragile or high-value items that will be stacked in a warehouse or on a pallet, prioritize ECT rating.

How to Choose the Right ECT Rating

Match your ECT rating to your product weight, fragility, and shipping environment:

• Under 20 lbs, standard products: 32 ECT is sufficient for most parcel shipments
• 20–50 lbs or fragile items: 44 ECT provides meaningful additional protection
• 50+ lbs or palletized freight: 48 ECT or double-wall construction
• Long transit times or humid environments: Consider double-wall regardless of weight — moisture weakens corrugated significantly

Don't Overlook Flute Type

ECT rating works alongside flute type — the internal wave structure of the corrugated board. Common flute types include:

• B flute — Thinner, good for printing and retail display
• C flute — Standard shipping flute, good balance of strength and cushioning
• BC flute (double-wall) — Maximum strength for heavy or high-value shipments

A 32 ECT C-flute box is the workhorse of e-commerce shipping. For most sellers, it's the right starting point.

Need help selecting the right box strength for your products? Browse our corrugated box inventory — our boxes are rated and labeled so you always know what you're getting.