Box Strength Ratings Explained: ECT vs. Mullen and How to Choose the Right Board

Buying corrugated boxes by size and price alone can leave your products vulnerable.
 

Every box carries a strength rating that tells you how much it can handle, but that number only helps when you know how to read it. Guess too low and your products get crushed. Guess too high and you pay for more boxes than you need. 

This article explains what ECT and Mullen ratings measure, how to find and read a box's strength rating, and how to match board strength to your products.

ECT vs. Mullen Box Strength Ratings: What's the Difference?
 

ECT and Mullen measure box strength in different ways. Understanding what each one tells you is the first step toward choosing the right board for your products. 

What a Mullen (Burst) Rating Measures

Mullen measures how much pressure a box wall can take before it bursts or punctures. It reflects resistance to impact and rough handling, which counts for heavy products or shipments that take a beating in transit. 

A higher Mullen rating points to a box that resists punctures from external forces. For items that face drops, jostling, or single-box shipping, burst strength is a reliable gauge of protection. 

What an ECT (Edge Crush Test) Rating Measures
 

ECT measures how much top-to-bottom pressure a box can withstand, which reflects stacking strength. It tells you how well a box holds up when other boxes are stacked on top of it.

A higher ECT rating points to a box that resists crushing under vertical weight. For boxes that spend time stacked in storage or on pallets, crush strength is the number that matters most. 

When to Use an ECT vs. a Mullen Box

For products that face rough handling or single-box shipping, Mullen strength is often the better gauge. For boxes that get stacked in storage or on pallets, ECT is the most useful number.

Many businesses ship and store, so understanding both ratings helps you pick the right box for each use. A product that ships individually has different needs than one that sits stacked in a warehouse for weeks. 

What a Box Maker's Certificate Stamp Tells You

Most corrugated boxes carry a round stamp called the box maker's certificate, usually printed on a bottom flap. This small stamp holds the information you need to match a box to your product before you ever load it.

The stamp lists the board's strength rating, either ECT or Mullen, along with size limits and the maximum weight the box is built to hold. Reading it tells you exactly what the box is rated for, so you're not guessing whether it can handle your product.

A box with no certificate gives you no documented proof of its strength, which makes it harder to match the box to your needs. When you compare options across suppliers, the certificate gives you measurable criteria. 

How to Match Box Strength to Your Product Weight
 

Heavier products need higher burst or crush ratings to avoid failure in transit. Matching strength to weight protects your products and keeps you from overpaying.
 

• Start with weight and shape. Sharp or dense items stress the box walls more than soft ones of the same weight. 
  
  
• Buy lighter for lighter products. Non-fragile, lightweight items don't need premium board strength.
   
• Size up when in doubt. For heavy or high-value items, a higher rating helps you avoid damage claims. 

Why Stacking and Storage Affect Box Strength

A box that performs well in single shipments can still collapse when stacked several units high. The boxes underneath carry the full downward weight of everything above them, which puts a different kind of stress on the board.

Stacking puts top-to-bottom pressure on a box, which is exactly what the ECT rating measures. Stacked loads depend on crush strength far more than burst strength, so a high Mullen rating won't protect a box at the bottom of a tall stack.

Storage adds stress over time. The longer boxes sit and the more humidity they absorb, the weaker the corrugated becomes. When stacking and storage go unaccounted for, the result is collapsed stacks, crushed products at the bottom, and safety hazards on the warehouse floor. 

Find the Right Box Strength with AM Shipping Supplies
 

At AM Shipping Supplies, we carry corrugated boxes across a range of ECT and Mullen ratings to match different product weights and stacking needs. We help you read the specs and pick the board strength that protects your products without paying for more than you need

Whether you're shipping heavy single items or stacking boxes in storage, we help you find the right box for the job.

Not sure which box strength your products need? Contact us at info@amshippingsupplies.com and we'll help you match the right board to your shipments.

Happy with the difference AM Shipping Supplies has made for your business? Leave a five-star review on Google to share your experience.