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Magnetic Box Board Thickness: How to Specify Greyboard for Rigid Boxes
Board thickness decides how a magnetic box behaves — not only how it feels. This guide covers what thickness actually controls, how millimetres and gsm relate, how to size board to box dimensions and contents, why hinge behaviour punishes over-specification, and the seven values a supplier needs before a thickness can be quoted accurately.
What this guide covers
Board thickness is usually treated as a quality signal — thicker reads as more premium. In production it is a structural variable. Changing it changes five things at once, and only one of them is perceived value.
Table 1: Five variables affected simultaneously by board thickness — the rows show common industry phenomena; actual behaviour varies with box type and process.
| Function | What happens when board is too thin | What happens when board is too thick |
|---|---|---|
| Rigidity / stacking | Side walls bow under stacking load; corners crush in the master carton. | Little additional benefit past the point where the box no longer deflects; cost rises. |
| Hinge behaviour | Lid creases irregularly; repeated opening softens the fold line. | Hinge resists folding and pushes the lid out of square (see the hinge section below). |
| Magnet performance | Board flexes, so magnets lose contact and the closure feels weak. | No functional gain; magnets sit further from the mating face. |
| Insert retention | Slots and platforms cannot hold their position under product weight. | Internal dimensions shrink, sometimes below the product tolerance. |
| Finished weight | Light — good for postage, poor for perceived value. | Freight and volumetric weight climb on every shipment, not just the first. |
The practical consequence is that thickness cannot be chosen alone. It has to be chosen together with box size, product weight, and how the lid is meant to move. A spec that only says “2 mm greyboard” leaves the factory to guess the rest — and two suppliers guessing differently will return two prices that are not comparable.
Two units appear in almost every rigid box specification, and they are not interchangeable. Thickness (mm) describes the caliper of the board. Grammage (gsm, g/m²) describes its mass per unit area. The relationship between them depends on board density, which varies by mill and by grade.
Greyboard (also called chipboard, or greyboard) typically falls in a density range around 0.6–0.75 g/cm³. That is why two boards quoted at “1200 gsm” can measure differently with a caliper — one is denser and therefore thinner.
Table 2: Approximate correspondence between greyboard thickness and grammage, used to convert a customer's mm requirement into a purchasing gsm, and vice versa.
| Typical thickness | Approx. grammage range* | Common application |
|---|---|---|
| 0.8 – 1.0 mm | 500 – 700 gsm | Small rigid lid-and-base boxes, jewellery and sample boxes |
| 1.2 – 1.5 mm | 800 – 1000 gsm | Standard cosmetic and small gift boxes up to ~150 mm |
| 1.8 – 2.0 mm | 1100 – 1300 gsm | Perfume boxes, mid-size rigid gift boxes, most magnetic closures |
| 2.5 mm | 1500 – 1600 gsm | Large-format boxes, shoe and apparel boxes, heavy contents |
| 3.0 mm | 1800 – 2000+ gsm | Oversized presentation boxes, wine and multi-product sets |
*Approximate conversion based on a board density near 0.65–0.70 g/cm³. Different mills and recycled-content grades will shift these figures — always confirm both values with your supplier rather than converting one from the other.
Specification
In the RFQ, state both thickness and grammage (for example, "2.0 mm greyboard, ≈1200 gsm"); this pins down the answer better than stating a single value.
When only gsm is stated, the supplier can meet the spec with lower-density board; when only mm is stated, the grammage may fall in an unexpected range. Stating both minimises the mismatch.
The useful starting point is not the box category — it is the longest side of the box and the weight it has to carry. A longer unsupported panel deflects more than a short one at the same thickness, so larger boxes need more board for the same perceived rigidity.
Table 3: Starting thickness recommendations by the box's longest side — this is a selection starting point, not the final specification.
| Longest side | Typical contents | Suggested starting board | Notes |
|---|---|---|---|
| Under 100 mm | Jewellery, sample vials, small electronics | 1.0 – 1.5 mm | Rigidity is rarely the constraint; surface finish drives perceived value. |
| 100 – 200 mm | Cosmetics, skincare, perfume | 1.5 – 2.0 mm | The most common range for magnetic closures. Check insert fit before locking the spec. |
| 200 – 300 mm | Apparel, accessories, multi-product sets | 2.0 – 2.5 mm | Side panels start to matter. Consider the stacking height in the master carton. |
| Over 300 mm | Shoes, large gift sets, outer presentation boxes | 2.5 – 3.0 mm | Weight becomes a freight decision as much as a design one. |
Starting point, not a specification
These ranges assume a product of moderate weight packed flat in a single layer. Heavy contents (glass bottles, ceramics, metal parts) or multi-level constructions generally move up one step. The reliable way to confirm is a physical sample loaded with the real product, not a calculation.
Glass is the common case. A 50 ml perfume bottle weighs roughly 150–200 g; a 100 ml bottle can exceed 300 g. Once the contents pass about 250–300 g, the weak point of a rigid box is usually not the side wall but the base panel and the insert that holds the bottle. Specifying thicker board all round often costs more than moving to a stronger insert — EVA or moulded pulp with a defined load path will usually outperform simply adding 0.5 mm of greyboard.
The board thickness you specify is not the wall thickness you receive. The finished wall is board + adhesive + wrapping paper, and the wrapping paper has its own caliper.
Wrapping also compresses the board. In production the combination of adhesive moisture, roller pressure and folding typically changes the finished dimension by a small but real amount — generally in the region of a few tenths of a millimetre per wall. That is well within normal die-cut tolerance (±0.5 mm is a common working figure for rigid box components), but it matters when internal clearance is tight.
The clearance trap
If your insert is designed to internal dimensions calculated from bare board thickness, the wrapped and assembled box will be tighter than the drawing. Always derive insert dimensions from a measured sample of the finished empty box, never from the board spec alone.
On a magnetic closure box the hinge is usually a scored or V-grooved line in the greyboard, wrapped over with paper. Thickness governs how cleanly that line folds — and this is where over-specifying backfires.
The same behaviour explains most lid-misalignment complaints that arrive after shipment. It is rarely a magnet problem and rarely a glue problem — it is usually the hinge fighting the board.
Board thickness is priced once, per unit. Freight is priced on every shipment, forever. For export orders the decision usually deserves to be made with both numbers in view.
Take a worked example. A box with 250 mm sides specified at 3.0 mm board instead of 2.0 mm adds roughly 1 mm to each of four walls. Depending on construction that can push the external dimension up by about 2 mm per axis. Individually trivial; across a master carton holding several dozen units it changes the outer carton size, and carton volume is what volumetric freight is calculated on for air shipments.
Table 4: Separate one-off cost from recurring cost — the layer most often overlooked in thickness decisions.
| Decision lever | Unit cost impact | Recurring impact |
|---|---|---|
| +0.5 mm board | Board cost per unit rises | None beyond unit price |
| Heavier unit | May move the shipment into a higher weight bracket | Every order, every reorder |
| Larger carton footprint | Changes how many units fit per carton | Every shipment |
| Volumetric vs actual weight | Determines which figure the carrier bills | Every air shipment |
From the factory floor
If this box will be reordered long term, we recommend making two thickness samples at the sampling stage, weighing them once loaded with the real product, then calculating the freight difference once for your actual shipping method (air / sea / express).
This difference is usually invisible on the first order, but by the third reorder it exceeds the cost difference of the board itself.
A thickness request that can be quoted accurately, and compared across suppliers, needs seven values. Anything less and you will receive numbers back that are not quotes — they are estimates with different assumptions baked in.
| Board type | Greyboard / chipboard, state grade and recycled content requirement if any |
| Thickness | In mm, with tolerance — e.g. 2.0 mm ±0.2 mm |
| Grammage | Corresponding gsm range, to lock density |
| Wrapping paper | Paper type and gsm — e.g. 157 gsm coated art paper |
| Box dimensions | External, plus required internal clearance for the product |
| Product weight | Actual weight in grams, loaded configuration |
| Closure & insert | Magnet count and position; insert type and how it carries the load |
If you can send the actual product, or a dimensionally identical dummy, do. Every parameter above becomes more accurate once the factory can put something real inside the box.
Board thickness for a magnetic box is not a quality setting — it is a structural and cost decision that touches rigidity, hinge behaviour, insert fit and freight at the same time. The most reliable sequence is to size the board to the box and its contents, verify it against a loaded physical sample, and only then adjust for cost. Specifying both millimetres and grammage is the cheapest way to make sure the sample you approve is the production you receive.
FAQ
How thick should the board be for a magnetic closure box?
Most magnetic boxes in the 100–200 mm range use board in the 1.5–2.0 mm band. Below about 100 mm, 1.0–1.5 mm is usually sufficient; above 300 mm, start at 2.5 mm. Treat these as starting points and confirm with the real product inside the box.
Is thicker board always better?
No. Past the point where the wall no longer deflects, additional thickness mainly adds weight and cost. On a hinged box it can actively worsen lid alignment, because the board resists the fold and holds the mating faces apart.
What is the difference between board thickness and gsm?
Thickness (mm) is caliper; gsm (g/m²) is mass per area. They are related through density, which varies by mill and grade. Quoting both removes the ambiguity — otherwise a supplier can satisfy one value while changing the other.
Why does my lid not sit flush even though the magnets are strong?
Look at the hinge before the magnet. If the board is too thick or the wrap direction works against the fold line, the hinge pushes back and the faces cannot meet, regardless of magnet strength.
How much do wrapping paper and glue add to the wall?
Small but measurable — generally a few tenths of a millimetre per wall from the paper caliper and adhesive, plus minor compression from wrapping pressure. Derive internal fit from a measured finished sample rather than from bare board.
Can I use the same board thickness for a folding carton?
No. Folding cartons use paperboard measured completely differently (typically 250–400 gsm folding box board) and score rather than V-groove. The thickness ranges in this article apply to wrapped rigid boxes only.
Specifying board thickness for a real project?
Send the box dimensions, product weight and target structure — we can cut the two candidate thicknesses, load them with your actual product, and let you compare before anything goes into production.
Request a QuoteReferences
The thickness values listed here are common industry ranges, offered as a reference starting point when drafting a specification; the actual specification should combine box type, contents weight and process, and be confirmed with a physical sample loaded with the real product.
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