Packaging & Box Strength formula solvers
Board Basis Weight (Grammage)
Packaging & Box StrengthMass divided by area — the way paper and combined board have always been sold, and the number that connects a blank size to a freight cost and a fibre bill. The whole difficulty is the units: grammage is grams per square metre almost everywhere, and North American board is quoted in pounds per thousand square feet, which is a different number for the same board.
Box Compression Service Derating
Packaging & Box StrengthThe chain of multipliers between a laboratory compression figure and the load a box will actually hold in a warehouse. Every factor on this page is a user input with NO default, on purpose. The circulating tables of humidity, storage-time, overhang and interlock numbers are unattributed restatements of a copyrighted handbook, and this site will not restate them either. What it will do is tell you what the open literature has measured, and warn you where the numbers everybody quotes have been shown to be wrong.
Box Perimeter
Packaging & Box StrengthThe distance around a rectangular box's footprint, and the Z that both McKee formulas want. It is deliberately not the girth used for shipping-size rules, and it takes no notice of the depth: what carries a top load is the four side panels standing on their edges, so the loaded length is the perimeter of the plan.
McKee Box Compression Formula (Long Form)
Packaging & Box StrengthMcKee's original and more general result, before caliper was substituted in as a proxy. It takes the board's measured bending stiffness in the machine and cross directions and uses their geometric mean, which is what the panel buckling analysis actually calls for. Use it whenever you have real stiffness data, and especially on board that has been crushed in converting, where caliper flatters the stiffness that is left.
McKee Box Compression Formula (Short Form)
Packaging & Box StrengthThe 1963 relation that turns an edge crush value, a board caliper and a box perimeter into the compression strength of a regular slotted container. It is the single most used equation in corrugated packaging, and the exponents are not the halves it is usually written with: 0.508 on caliper and 0.492 on perimeter, chosen so the constant 5.874 comes out a pure number that works in any consistent unit system.
Ring Crush to Edge Crush (Whitsitt Relation)
Packaging & Box StrengthAn empirical regression that estimates the edge crush value of combined board from the ring crush values of the liners and the medium that went into it. Useful when the components were tested and the combined board was not — and carrying one honest ugliness: unlike McKee's constants, this one has an ADDITIVE term, so it is unit-bound in a way no choice of exponent can fix.
Shallow Box Validity Check for McKee
Packaging & Box StrengthMcKee's formula assumes the box fails by its side panels buckling, and a box has to be deep enough for panels to buckle. Below a depth of about the perimeter divided by seven they do not — the panels crush in compression instead, the caliper term stops meaning anything, and the equation is wrong in FORM rather than merely out of calibration. This ratio is one when the box sits exactly on that limit.
Stack Load on the Bottom Case
Packaging & Box StrengthWhat the bottom case in a stack actually carries: every case above it, and not its own weight. The minus one is the whole content of the equation and it is the term most often got wrong — a six-high stack puts five cases on the bottom one, not six.
Stacking Safety Factor
Packaging & Box StrengthThe ratio of what the box can carry to what the stack puts on it. Simple arithmetic with a hard warning attached: a safety factor applied on top of a full chain of derate multipliers double-counts, because the multipliers already contain most of the margin the trade rule was invented to supply.