Box compression estimate

What the calculator estimates

The calculator has one job: turn a small set of package and board inputs into a short-term compression estimate and a planning load. The four result rows are estimated short-term BCT in pounds-force, derated planning load in pounds-force, whole cases above the bottom case, and total theoretical stack. The first two rows are loads; the second two are counts derived from the loaded case weight.

This is an empirical RSC estimate. It is not a tested safe load, and the output is not a certification of package performance.

Inputs that drive the estimate

Use length and width for the case footprint in inches. The formula forms perimeter as 2 times the sum of length and width, so these two fields describe the footprint used for the compression estimate. Enter edge crush in pounds per inch and board thickness, called caliper, in inches. The loaded case weight is used only when converting the planning load into a case count.

The planning derating factor is a divisor chosen by the user. A factor of 1 applies no derating; larger factors reduce the planning load. The starting factor of 5 is a scenario value, not a recommendation for a particular warehouse, route or storage duration.

How the BCT equation works

The calculator uses a simplified McKee relationship: BCT equals 5.87 times edge crush times the square root of (caliper times perimeter). Perimeter is 2 times the sum of length and width. So edge crush acts as a direct multiplier. Increasing edge crush from 32 to 64 lb/in would double the estimated BCT if all other inputs stayed fixed.

Caliper and footprint do not act as direct multipliers. They sit inside the square root, so their effect is smaller and nonlinear. Doubling caliper alone multiplies the estimate by about the square root of 2, not by 2.

Converting BCT to a planning load

The derated planning load is the estimated short-term BCT divided by the planning derating factor. The factor changes the planning load and can change both derived stack counts, but it does not change the BCT row. A factor of 5 leaves one fifth of the estimate; a factor of 10 leaves one tenth. This division is a planning step, not a test result and not a guarantee of stack performance.

Counting cases in the theoretical stack

Whole cases above the bottom case equals floor of the derated planning load divided by loaded case weight. The floor operation truncates any fractional case, so the count never rounds up. Total theoretical stack adds one for the bottom case. If the derated load is less than one loaded case weight, the whole-cases-above result is zero and the total is one. These counts are arithmetic outputs, not a safe stack height. Height, cutouts, humidity, creep, pallet support and workmanship can invalidate the model.

Worked case: 32 ECT, 0.157 in board, 12 by 10 in footprint

With length 12 in, width 10 in, edge crush 32 lb/in, caliper 0.157 in, factor 5 and loaded case weight 20 lb, the calculator forms perimeter 44 in. The estimated short-term BCT is about 493.7 lbf. The derated planning load is about 98.74 lbf. Dividing 98.74 by 20 gives 4.937, which floors to 4 whole cases above the bottom case. Adding the bottom case gives a total theoretical stack of 5. The displayed BCT and planning load are rounded for display; use them as model outputs, not extra precision.

Worked case: change only the derating factor

Keep the same length, width, edge crush, caliper and 20 lb loaded case weight, but change the planning derating factor from 5 to 10. The BCT remains about 493.7 lbf because the factor does not enter the compression equation. The derated planning load falls to about 49.37 lbf. Dividing by 20 gives 2.468, which floors to 2 whole cases above the bottom case, and the total theoretical stack becomes 3. Doubling the factor halves the planning load and can reduce the count by a whole case or more.

Rounding, edge cases and validation

Stack counts use floor, so a small change in the derated load or loaded case weight can cross an integer boundary and change the count by one. If loaded case weight is greater than the derated load, the whole-cases-above count is zero and the total is one. If the loaded case weight is very low, the count can grow quickly even though the load estimate has not changed. The model does not explain height, cutouts, humidity, creep, pallet support or workmanship, and those factors can invalidate the estimate. Validate the finished pack with physical compression testing; ASTM D642 describes compression testing of shipping containers.

Questions about box compression estimate