Shipping Boxes
What Makes a Good Shipping Box?
A shipping box has one job: get your product from point A to point B undamaged. But within that simple goal lies a set of engineering decisions — box size, wall construction, crush strength, material quality, and closure method — that directly impact your product safety, shipping costs, and customer satisfaction.
Shipping Box Strength Ratings
Two common measurements define a shipping box's strength:
Edge Crush Test (ECT)
Measures the box's resistance to crushing when stacked. ECT is the current industry standard for specifying corrugated strength. Common ECT values:
| ECT Rating | Max Product Weight | Typical Application |
|---|---|---|
| 32 ECT | Up to 40 lbs | Standard shipping, light to medium products |
| 44 ECT | Up to 65 lbs | Heavier products, stacking in warehouses |
| 48 ECT | Up to 80 lbs | Heavy items, industrial parts |
| 51 ECT (DW) | 80-120 lbs | Double wall, heavy-duty applications |
| 71 ECT (DW) | 120+ lbs | Very heavy items, machinery components |
Burst Strength (Mullen Test)
Measures resistance to puncture — how much pressure the box can withstand before rupturing. While ECT is more commonly specified today, burst strength is still relevant for applications where rough handling or puncture risk is a concern.
Shipping carriers now calculate charges based on DIM weight (dimensional weight) — essentially charging you for the space a package occupies, not just its actual weight. Using a box that's too large means you're paying to ship air. Right-sizing your shipping boxes can reduce shipping costs by 10-25%.
Carrier Size Guidelines
| Carrier | Max Size (Standard) | Oversize Threshold |
|---|---|---|
| USPS Priority Mail | Any size (weight limits) | Varies by service |
| UPS Ground | 108" combined L+girth | 96" length |
| FedEx Ground | 108" combined L+girth | 96" length |
| LTL Freight | Pallet-based | Varies by carrier |
Types of Shipping Boxes
RSC (Regular Slotted Container) — The most common and economical. All four flaps are the same length. Ideal for most general shipping.
Telescoping Boxes — A separate top and bottom that overlap. Used for tall, narrow items or products requiring extra stacking protection.
Mailer Boxes — One-piece boxes with a tuck-front lid. Popular for e-commerce and subscription boxes. See our mailer boxes page.
Multi-Depth Boxes — Scored at multiple heights so you can fold down to the exact height needed. Reduces the need to stock many different box sizes.
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