Resources & Guides
Two technical references for specifying paper and board: how to convert paper weight between gsm and US basis weights, and how the four main board families differ in fibre, surface and end use. Both are general industry references rather than a list of our stock. For a specification on a particular grade, ask us.
How Do You Convert Paper Weight Between gsm and US Basis Weight?
Divide by the paper's basic size. Grammage in grams per square metre is an absolute measure, but a US basis weight is the weight of 500 sheets at that grade's own basic sheet size, so the same pound figure means a different thickness depending on whether the stock is text, cover or bond. The formula below converts in either direction, and the tables give the common values.
The Conversion Formula
To convert a US basis weight to grammage, multiply the pound figure by 1,406.5 and divide by the area of that grade's basic sheet in square inches:
gsm = lb × 1,406.5 ÷ (basic sheet width × height in inches)
To go the other way, rearrange: lb = gsm × (width × height) ÷ 1,406.5. The constant 1,406.5 converts 500 sheets measured in square inches and pounds into a single square metre measured in grams.
Basic Sheet Sizes by Grade
The basic size is fixed per grade by convention, not by the sheet you are buying. This is the step most often missed when comparing a US specification with a European one.
| Grade | Basic size (in) | Area (sq in) | lb to gsm multiplier |
|---|---|---|---|
| Text and book | 25 × 38 | 950 | 1.480 |
| Cover | 20 × 26 | 520 | 2.705 |
| Bond and writing | 17 × 22 | 374 | 3.761 |
| Bristol | 22.5 × 28.5 | 641 | 2.194 |
| Index | 25.5 × 30.5 | 778 | 1.808 |
| Tag | 24 × 36 | 864 | 1.628 |
Common Text and Book Weights
| US basis weight (lb) | Grammage (gsm) |
|---|---|
| 50 | 74 |
| 60 | 89 |
| 70 | 104 |
| 80 | 118 |
| 100 | 148 |
| 110 | 163 |
Common Cover Weights
| US basis weight (lb) | Grammage (gsm) |
|---|---|
| 65 | 176 |
| 80 | 216 |
| 100 | 270 |
| 110 | 298 |
| 130 | 352 |
Common Bond and Writing Weights
| US basis weight (lb) | Grammage (gsm) |
|---|---|
| 20 | 75 |
| 24 | 90 |
| 28 | 105 |
| 32 | 120 |
Grammage figures are rounded to the nearest whole gsm. Mill tolerances mean a delivered reel or pallet will vary slightly around its nominal grammage; where a specification is critical, work from the mill's own datasheet for the specific grade.
Which Board Grade Should You Specify?
Board grade is chosen by fibre composition and surface, not by weight alone. The four families below cover most UK packaging work. Solid bleached board gives the highest purity and print surface at the highest cost; folding boxboard gives the best stiffness for its weight; white lined chipboard is the economical recycled option; solid unbleached board is the strength choice. The table sets out what each is made from and where it is normally used.
| Family | Grade codes | Fibre composition | Surface and print | Typical end uses |
|---|---|---|---|---|
| Solid bleached board (SBB, also SBS) | GZ | Bleached chemical pulp throughout, no recycled content | Highest brightness and purity; coated one or two sides; excellent for fine screen and foil work | Cosmetics and fragrance, pharmaceutical cartons, premium confectionery, direct food contact |
| Folding boxboard (FBB) | GC1, GC2 | Multi-ply: bleached chemical pulp outer plies with a mechanical pulp middle ply | Coated top; GC1 has a cream or unbleached reverse, GC2 a white reverse. High stiffness for its weight because the bulky middle ply sits away from the neutral axis | The general-purpose carton board: food and beverage, healthcare, greeting cards, general retail |
| White lined chipboard (WLC) | GD1, GD2, GD3, GT1 | Predominantly recycled fibre with a bleached white top liner | Coated white top over a grey reverse; good general print surface, lower brightness than virgin grades | Dry foods, detergents and household goods, shelf-ready packaging, cost-sensitive retail cartons |
| Solid unbleached board (SUB) | UD, UZ | Unbleached kraft chemical pulp | Natural brown unless coated; the highest tear and wet strength of the four | Beverage multipacks, chilled and frozen packs, heavy-duty and moisture-exposed applications |
What the Grade Codes Mean
The GC, GD, GT and UD codes are the European convention for describing board construction. The first letter indicates the top ply, the second the reverse and the general construction, and the number the quality tier within that family, with 1 being the highest. GC1 and GC2 are both coated folding boxboard; they differ in the reverse side, which is why GC2 is specified where the inside of a carton is visible in use.
Choosing Between Virgin and Recycled Fibre
Virgin grades are specified where purity, brightness or direct food contact govern the choice. Recycled grades are specified where cost and recycled content govern it. Both are recyclable at end of life, and recycled content alone is not a reliable proxy for environmental performance: transport distance, coating and the number of times the fibre has already been through the loop all bear on it. Where a brand needs to state recycled content on pack, the mill's own declaration is the document that supports the claim.
Datasheets
Manufacturer datasheets for two folding boxboard grades we hold:
These two pages are a general reference to how the grades are defined across the industry, not a statement of what we currently hold. For grammage, caliper, brightness and availability on a specific grade, ask us for the current specification.
Reducing Waste in Paper and Board Supply
Responsible sourcing is central to how we operate, and we back it up with practical waste reduction: converting to size to avoid offcuts, reworking and reissuing redundant stock, and planning logistics to minimise unnecessary mileage.
Ready to Discuss Your Requirements?
Whether you need a quote, technical advice or want to explore how we can support your supply chain, get in touch and we will respond promptly.
Request a Quote