Input data
Storage and delivery conditions
Load parameters
BCT
General engineering allowance for uncertainty, dynamics, production variation and decision responsibility. If humidity is already covered here, do not duplicate it with high BCT reduction.
BCT (McKee)
Allowed load
Learn
How the box compression calculator works
From the board and the box size to the box compression strength (BCT), the load one box may carry and the number of boxes a column can hold.
What it calculates
The calculator estimates box compression strength (BCT), the top-to-bottom load a corrugated box withstands, with the simplified McKee formula from three inputs: the edge crush strength of the board (ECT), the wall thickness and the box perimeter. Choosing a flute and a catalogue grade fills in a typical ECT and thickness; the value from the board supplier’s data sheet replaces them.
Humidity, transport mode and storage time weaken a box. Each is a multiplier, and together they become the BCT reduction. The reduced strength divided by the safety factor is the load one box may carry, and from the filled box mass the calculator gives the number of boxes a column can hold, the bottom box included.
The same stacking limit feeds the palletizer as its column height cap, so a pallet pattern cannot stack boxes higher than their board allows.
Standards and methods behind it
- McKee formula (simplified): BCT from ECT, wall thickness and perimeter.
- TAPPI T 804: the compression test that defines BCT. The calculator estimates that number; it does not replace the test.
- ISO 3037: the edgewise crush test behind the ECT of the DIN board grades; the GOST R 52901 grades T-21 … T-34 form the second board table.
Worked example
A 400 × 300 mm box of 1.30 C board (C flute), 10 kg filled, with the palletizer defaults: 20 % BCT reduction and safety factor 6.
In the calculator: C flute, ECT 4.5 kN/m typed by hand and a 20 % reduction typed by hand, instead of the values the form fills in by default.
1. Box perimeter
Z = 2 × (400 + 300) = 1,400 mm
2. Box compression strength by McKee
ECT = 4.5 kN/m, t = 4 mm; BCT = 5.876 × 4.5 × √(4 × 1,400) = 1,979 N
3. Strength after the reduction for conditions
BCT_r = 1,979 × (1 − 20 / 100) = 1,583 N
4. Load one box may carry
P = 1,583 / 6 = 263.8 N → 26.9 kg
5. Boxes in a column, the bottom one included
n = ⌊26.9 / 10⌋ + 1 = 3
A column of 3 boxes is the most this box can stack with these allowances; the palletizer takes the same number as its column limit.
A 15.75 × 11.81 in box of 1.30 C board (C flute), 22 lb filled, with the palletizer defaults: 20 % BCT reduction and safety factor 6.
In the calculator: C flute, ECT 25.7 lbf/in typed by hand and a 20 % reduction typed by hand, instead of the values the form fills in by default.
1. Box perimeter
Z = 2 × (15.75 + 11.81) = 55.12 in
2. Box compression strength by McKee
ECT = 25.7 lbf/in, t = 0.1575 in; BCT = 5.876 × 25.7 × √(0.1575 × 55.12) = 445 lbf
3. Strength after the reduction for conditions
BCT_r = 445 × (1 − 20 / 100) = 356 lbf
4. Load one box may carry
P = 356 / 6 = 59.3 lbf → 59.3 lb
5. Boxes in a column, the bottom one included
n = ⌊59.3 / 22⌋ + 1 = 3
A column of 3 boxes is the most this box can stack with these allowances; the palletizer takes the same number as its column limit.
The results are the calculator’s own for these inputs; converted and rounded figures can differ in the last digit.
Common mistakes
- Mixing units in McKee: ECT in N/m with millimetres is off by a factor of 1000. Keep ECT in kN/m with millimetres, or in N/m with metres.
- Counting humidity twice: a high safety factor together with a large reduction for humidity makes a box look far weaker than it is. The calculator warns when both are high.
- Taking the ECT of the grade instead of the supplier’s data sheet: catalogue values are typical, and the board you buy can be weaker.
- Ignoring overhang and shifted columns: a box that overhangs the pallet or stands on a brick joint loses strength the formula does not see.
When this tool is not the right one
- Proof of compliance: the result is an engineering estimate, not a test report. Approve the packaging with a compression test.
- Boxes that are not regular slotted containers: die-cut trays, boxes with inserts or dividers, and products that carry part of the load are outside the formula.
- Solid board, plastic and wooden crates: McKee is a relation for corrugated board.
Questions
What is BCT?
Box compression test: the load, in newtons or pounds-force, under which an empty box collapses when pressed top to bottom. It is the property that decides how high boxes can be stacked.
What is the McKee formula?
A relation published by McKee, Gander and Wachuta in 1963 that estimates BCT from the edge crush strength of the board, its thickness and the box perimeter. The simplified form multiplies a constant by ECT and by the square root of wall thickness times perimeter; the constant and the units are on the method page.
Which safety factor should I use?
It depends on how long the boxes stand and how they are handled. The calculator starts from its default and warns when the safety factor and the reduction for conditions look like they count the same risk twice.
How do I convert ECT between kN/m and lb/in?
1 kN/m is about 5.71 lbf/in, so 7 kN/m is about 40 lbf/in — the “40 ECT” grade used in North America.
Every formula with its units and defaults: the calculation method →