Understanding Corrugated Box Strength and ECT

What is ECT (Edge Crush Test)?

Edge Crush Test (ECT) measures how much top-to-bottom pressure a corrugated box can withstand before collapsing. It's the most important specification for determining if your boxes will survive stacking, shipping, and storage.

ECT Ratings Explained

ECT is measured in pounds per linear inch (lbs/in). Common ratings:

23 ECT - Light Duty

• Stacking strength: Can support approximately 20-25 lbs
• Best for: Lightweight products, short-term storage
• Common uses: Gift boxes, retail displays, clothing
• Cost: Most economical option

32 ECT - Standard

• Stacking strength: Supports 50-65 lbs
• Best for: Most e-commerce applications
• Common uses: Books, small electronics, housewares
• Sweet spot: Balance of strength and cost

44 ECT - Heavy Duty

• Stacking strength: Supports 80-95 lbs
• Best for: Heavier products, long-distance shipping
• Common uses: Appliances, bulk orders, warehouse storage
• Cost: 15-20% more than 32 ECT

51+ ECT - Extra Heavy Duty

• Stacking strength: 100+ lbs
• Best for: Industrial applications, export
• Common uses: Machinery parts, automotive, international shipping
• Cost: Premium pricing but essential for heavy loads

Factors Affecting Box Strength Beyond ECT

1. Box Design

Design impacts structural integrity:

• Regular Slotted Container (RSC): Most common, good all-around strength
• Full Overlap: Stronger bottom, better for heavy products
• Half Slotted: Open top, less structural strength
• Die-cut designs: Custom shapes may sacrifice strength

2. Flute Type

Flute refers to the wavy layer between box walls:

• A-flute: Thickest (5mm), best cushioning, lower stacking strength
• B-flute: Thin (3mm), excellent printing surface, good crush resistance
• C-flute: Medium (4mm), most popular, balanced properties
• E-flute: Very thin (1.5mm), retail packaging, printability

3. Environmental Factors

Conditions affect box performance:

• Humidity: High moisture reduces strength by up to 50%
• Temperature: Extreme heat weakens adhesives
• Storage duration: Prolonged storage degrades strength
• Compression time: Long-term stacking reduces capacity

Calculating Required ECT for Your Products

Use this formula as a starting point:

1. Product weight: Weigh your product plus inner packaging
2. Box dimensions: Measure length, width, height
3. Stacking height: How high will boxes stack? (warehouse or shipping)
4. Safety factor: Multiply by 1.5-2x for safety margin

Example calculation:

Product weight: 5 kg (11 lbs)
Expected stacking: 5 boxes high
Total load: 11 lbs × 5 = 55 lbs
Safety factor: 55 × 1.5 = 82.5 lbs
Recommended ECT: 44 ECT

ECT vs. Mullen (Burst) Test

Two main standards exist:

ECT (Edge Crush Test)

• Modern standard, more relevant for shipping
• Measures vertical compression strength
• Better predictor of real-world performance
• Preferred by carriers and logistics

Mullen Test

• Older standard, measures burst strength
• Tests resistance to puncture pressure
• Still used for some international shipping
• Less relevant for stacking scenarios

Unless specifically required, ECT is the better choice for most applications.

Common ECT Selection Mistakes

1. Under-specifying for Cost Savings

Choosing 23 ECT instead of 32 ECT to save ₹2 per box, then dealing with:

• Damaged products worth ₹1,000+
• Return shipping costs
• Customer service time
• Negative reviews

Result: "Savings" of ₹2,000 cost ₹50,000+ in damages and lost customers

2. Ignoring Stacking Requirements

Box survives shipping but collapses in warehouse when stacked 8 high. Consider entire supply chain, not just delivery.

3. Not Testing in Real Conditions

ECT ratings assume ideal conditions. Test boxes in actual humidity and temperature before bulk orders.

Industry-Specific ECT Guidelines

E-commerce

• Apparel: 23-32 ECT
• Books/Media: 32 ECT
• Electronics: 32-44 ECT
• Housewares: 32-44 ECT
• Appliances: 44-51 ECT

Food & Beverage

• Dry goods: 32 ECT
• Canned goods: 44 ECT
• Glass bottles: 44-51 ECT
• Frozen foods: 51+ ECT (moisture resistance critical)

Industrial

• Parts/Components: 44 ECT minimum
• Machinery: 51+ ECT
• Export shipments: 51+ ECT (long journey, multiple handlers)

Testing Your Box Strength

Before committing to large orders:

1. Sample test: Order samples, test with actual products
2. Drop test: Drop from waist height multiple times
3. Stacking test: Stack boxes at expected height for 24+ hours
4. Environmental test: Test in hot warehouse or humid conditions
5. Shipping test: Ship to yourself via normal route

Quick ECT Decision Guide

Choose 23 ECT if:

• Products under 5 lbs
• Hand-delivered or minimal shipping
• Not stacked during storage
• Short-term use only

Choose 32 ECT if:

• Products 5-15 lbs (most e-commerce)
• Standard courier shipping
• Moderate stacking (3-4 boxes high)
• Normal warehouse conditions

Choose 44 ECT if:

• Products 15-30 lbs
• Long-distance shipping
• High stacking (5-8 boxes)
• Humid or rough conditions

Choose 51+ ECT if:

• Products 30+ lbs
• International shipping
• Industrial applications
• Maximum protection required

Still unsure? Contact BoxFold for a free consultation. We'll analyze your specific needs and recommend the optimal ECT rating that balances protection and cost.