Design & Printing Tools

Paperboard Thickness & GSM Calculator

Q: Is a "PT" the same as a typographic point?

No. A caliper point (PT) is one thousandth of an inch — 1 PT = 0.0254 mm, so 12 PT is about 0.3 mm. A typographic point is 1/72 inch and is used for type sizes, not board thickness. When a US supplier says "18 pt board" they mean caliper.

Q: What thickness should I use for a folding carton?

300–350 GSM (roughly 0.40–0.47 mm) suits most cosmetic, supplement and retail cartons. Use 250 GSM for light, low-cost cartons that ship inside another box, and 400 GSM when the carton must hold its shape on a shelf or carry a premium price point.

The same board is quoted three ways: GSM in Asia, PT (points) in the USA, millimetres on a technical drawing. Convert between all three and see the caliper to expect for SBS white card, art paper, kraft and greyboard — before you sign off a spec.

Board type

Value

Unit

Common weights:

Grammage350g/m²

Caliper0.47mm

Points18.3PT

Typical caliper for the selected board. Real thickness moves with grade, coating and moisture — expect roughly ±5–10% between mills. Always confirm against a physical sample before you approve artwork.

One unit does not convert to another on its own: GSM is weight and PT/mm are thickness. The bridge is the board's bulk (volume per gram). We use typical bulk values — SBS C1S 1.33, C2S 1.25, art paper 1.20, woodfree 1.30, kraft 1.50, greyboard 1.60 cm³/g — so caliper (mm) ≈ GSM × bulk ÷ 1000. PT is exact: 1 PT = 0.0254 mm.

Typical Caliper by Board Type

Reference values for the boards we run every day. Use the calculator above for other combinations; treat this chart as a starting point for spec sheets and quotes, not a guarantee.

Board	GSM	Caliper (mm)	PT
SBS C1S white card	250	0.33	13.1
SBS C1S white card	300	0.40	15.7
SBS C1S white card	350	0.47	18.3
SBS C1S white card	400	0.53	20.9
SBS C2S (coated two sides)	200	0.25	9.8
SBS C2S (coated two sides)	250	0.31	12.3
SBS C2S (coated two sides)	300	0.38	14.8
SBS C2S (coated two sides)	350	0.44	17.2
SBS C2S (coated two sides)	400	0.50	19.7
Coated art paper	128	0.15	6.0
Coated art paper	157	0.19	7.4
Coated art paper	200	0.24	9.4
Coated art paper	250	0.30	11.8
Coated art paper	300	0.36	14.2
Coated art paper	350	0.42	16.5
Uncoated woodfree	100	0.13	5.1
Uncoated woodfree	120	0.16	6.1
Uncoated woodfree	150	0.20	7.7
Uncoated woodfree	200	0.26	10.2
Uncoated woodfree	250	0.33	12.8
Uncoated woodfree	300	0.39	15.4
Kraft board	200	0.30	11.8
Kraft board	250	0.38	14.8
Kraft board	300	0.45	17.7
Kraft board	350	0.53	20.7
Greyboard (rigid box board)	1000	1.60	63.0
Greyboard (rigid box board)	1200	1.92	75.6
Greyboard (rigid box board)	1500	2.40	94.5
Greyboard (rigid box board)	1800	2.88	113.4

How to Choose the Right Thickness

Thicker is not automatically better. Heavier board stiffens a box and raises the perceived value, but it also costs more, folds less cleanly and adds freight weight. Match the board to the structure and the job it has to do.

Folding cartons (tuck-end, auto-lock, sleeves)

250–400 GSM white card (SBS C1S) is the workhorse. 300–350 GSM covers most cosmetics, supplements and retail cartons; go to 400 GSM when the carton has to stand unsupported on a shelf or feels premium in the hand. Below 250 GSM the panel flexes and the creases look soft.

Rigid boxes (magnetic closure, book-style, drawer)

The stiffness comes from the greyboard core, 1000–1800 GSM (≈1.6–2.9 mm), then a 128–157 GSM printed wrap. 1200 GSM is our most common core for gift boxes; 1400 GSM and up for watch, jewellery and heavier electronics.

Corrugated mailers

Corrugated is graded by flute, not GSM. E-flute (≈1.5 mm) prints well and is the usual choice for printed mailer boxes; thicker flutes add stacking strength for export cartons. See the corrugated mailers range.

Kraft and eco boxes

250–350 GSM kraft board reads natural and folds well; heavier grades for hardware and tools where burst strength matters more than looks. See Eco Kraft Boxes.

Want the full picture of how these boards behave — inside liner, coating, food contact? Read Paper Box Materials Explained, or check how finishes interact with the board in Printing Service. If you already have artwork, the free dieline service gives you the right structure for the board you pick.

FAQ

Is a "PT" the same as a typographic point?

No. A caliper point (PT) is one thousandth of an inch — 1 PT = 0.0254 mm, so 12 PT is about 0.3 mm. A typographic point is 1/72 inch and is used for type sizes, not board thickness. When a US supplier says "18 pt board" they mean caliper.

Can I convert GSM to PT exactly?

Not from GSM alone. GSM is weight per square metre; PT and mm are thickness. The link between them is the board's bulk, which changes with furnish, coating and how hard the sheet is calendered. Two boards both marked 350 GSM can differ by 0.05 mm or more. Use this calculator for a working estimate, then confirm the actual caliper with a sample.

How does GSM relate to the US "lb" (text / cover) system?

They measure different things on different base sheets, so there is no single multiplier. US "lb" is the weight of 500 sheets at that grade's base size, which varies by paper type. For packaging the practical answer is to work in GSM or in caliper (PT/mm) and ignore lb unless your printer only quotes that way.

What thickness should I use for a folding carton?

300–350 GSM (roughly 0.40–0.47 mm) suits most cosmetic, supplement and retail cartons. Use 250 GSM for light, low-cost cartons that ship inside another box, and 400 GSM when the carton must hold its shape on a shelf or carry a premium price point.

Can you hold an exact caliper tolerance on my order?

Yes, within reason. We can agree a working range (for example 0.45–0.49 mm for a 350 GSM spec) before production. If your structure or machine needs a tight window, tell us the target and the acceptable range when you request the quote and sample.

Not Sure Which Board Fits Your Box?

Send us the product, the box structure and where it will be sold. We'll recommend a board and thickness, then post a physical sample within 3–5 working days.

Ask for a Thickness Recommendation →