Want this on your own domain?
We build this calculator as an embeddable tool — engineered, SEO- and AI-ready, delivered in 5 business days for a flat $2,800.
Get yours in 5 daysHow it's calculated
Box Compression Test (BCT) is the top-to-bottom load a carton survives. The McKee formula estimates it from three things: the board’s edge crush (ECT), its thickness (caliper) and the box perimeter (2 × [L + W]). The result is a lab-fresh, brand-new-box number — real stacks lose strength to time, humidity and pallet overhang, so a safety factor converts BCT into a load the bottom box can actually hold.
- 12 × 10 × 8 in, 32 ECT, caliper 0.16 in.
- Perimeter = 44 in; √(0.16 × 44) = 2.65.
- BCT = 5.87 × 32 × 2.65 ≈ 498 lb fresh.
- At a 5× safety factor, safe stacking ≈ 100 lb.
Reference tables
Common board ECT and caliper
| Board | ECT (lb/in) | Caliper (in) |
|---|---|---|
| Single-wall B-flute | 26–32 | 0.09 |
| Single-wall C-flute | 29–32 | 0.16 |
| Single-wall BC skip | — | 0.16 |
| Double-wall BC | 44–51 | 0.25 |
| Double-wall EB | 32–40 | 0.19 |
Safety factor by storage condition
| Condition | Factor |
|---|---|
| Fast turn, controlled RH | 3–4 |
| Typical warehouse | 4–5 |
| Long storage / high humidity | 6–7 |
A number the tables do not give: a 12×10×8 in box on 32 ECT C-flute tests near 500 lb BCT, so a 5× factor leaves about 100 lb of safe stacking load.
See a live tool in action
This calculation is exactly what our packaging / box simulator runs live. Open it to see how the same inputs become a cut plan, stacking strength and pallet fit on your own domain:
FAQ
What is the difference between ECT and BCT?
ECT is a board property — how much edge crush the corrugated withstands per inch. BCT is the whole box’s top-load strength. McKee links them using the box perimeter and board caliper.
Why apply a safety factor?
BCT is measured on a fresh, perfect box. Humidity can cut strength by half, and stacking time, vibration and pallet overhang all erode it. The factor keeps the bottom box safe over its real life.
Does humidity really matter that much?
Yes. Corrugated loses roughly 15% strength for every step up in relative humidity band; at very high RH a box can hold under half its dry BCT. Size for the worst case in your supply chain.
How do I raise box strength cheaply?
Reduce perimeter (a squarer footprint), step up ECT, or align load-bearing on the corners where the box is strongest — often cheaper than jumping to double-wall.
Build it for your catalog
Put this calculator on your domain so the engineers who run it land on your site — not a competitor's. See how it works or start the conversation.