Paper Weight Guide: GSM, lb and thickness explained

 

Paper weight is measured in gsm (grams per square meter) in most of the world. US printers use pounds (lb). To convert, multiply lb text by 1.48 or lb cover by 2.704 to get gsm. GSM tells you how heavy the paper is, not how thick it is. Two 300 gsm papers can differ in thickness by more than 80%.

This guide uses the official basis sizes to calculate conversions and manufacturer datasheets to show how weight and thickness relate. It also corrects two mistakes found in pages that currently rank for paper weight searches.

 

What gsm measures

GSM is the mass of one square meter of a single sheet. An A4 sheet is 0.0624 m², so:

• An 80 gsm A4 sheet (standard office paper) weighs 5.0 g
• A 300 gsm A4 sheet (business card stock) weighs 18.7 g

GSM is the same unit for every kind of paper. A 120 gsm sheet is always heavier than a 100 gsm sheet, whatever it is called.

 

Why US pound weights are confusing

The US system gives the weight in pounds of 500 sheets (a ream) at a "basis size." Each paper category uses a different basis size, so the same paper gets a different number depending on its category.

Basis sizes and conversion factors:

• Bond (office, writing): 17 × 22 in. 1 lb = 3.760 gsm
• Text/Book (flyer and brochure pages): 25 × 38 in. 1 lb = 1.480 gsm
• Cover (card stock): 20 × 26 in. 1 lb = 2.704 gsm
• Index: 25.5 × 30.5 in. 1 lb = 1.808 gsm
• Bristol: 22.5 × 28.5 in. 1 lb = 2.193 gsm

We calculated these from the basis sizes: 1 lb is 453.592 g, divided by the area of 500 sheets in square meters.

The result: a 120 gsm sheet is 32 lb bond, 81 lb text, or 44 lb cover. Same paper, three numbers. When you order in the US, the category matters as much as the number.

 

GSM to lb conversion chart

Text weights (for flyers, brochure pages, letterheads):

• 80 gsm = 54 lb text = 21 lb bond
• 90 gsm = 61 lb text = 24 lb bond
• 100 gsm = 68 lb text = 27 lb bond
• 115 gsm = 78 lb text
• 120 gsm = 81 lb text = 32 lb bond
• 130 gsm = 88 lb text
• 150 gsm = 101 lb text
• 170 gsm = 115 lb text

Cover weights (for covers, postcards, business cards):

• 200 gsm = 74 lb cover
• 250 gsm = 92 lb cover
• 300 gsm = 111 lb cover
• 350 gsm = 129 lb cover
• 400 gsm = 148 lb cover

Printers round these to catalogue weights. A "100 lb cover" is sold as 270 to 275 gsm, and an "80 lb text" as 118 to 120 gsm.

 

A common chart mistake: 300 gsm is not 202 lb

At least one ranking conversion chart lists "300 gsm = 202 lbs." The math is correct only for the text basis size. Nobody sells 202 lb text. Paper that heavy is card stock, sold by cover weight, where 300 gsm is 111 lb cover.

If you ask a US printer for 202 lb paper, they will not know what you mean. Ask for 110 or 111 lb cover, or give the gsm.

 

GSM is not thickness

Thickness depends on weight and on density. Paper mills publish both. Here is what 300 gsm looks like across five real papers, from the manufacturers' datasheets:

• Sappi Magno Gloss (coated gloss): 228 µm, 9.0 pt
• Sappi Magno Satin (coated silk): 282 µm, 11.1 pt
• Sappi Magno Matt (coated matte): 309 µm, 12.2 pt
• Arctic Paper Munken Pure (uncoated): 339 µm, 13.3 pt
• Arctic Paper Munken Pure Rough (uncoated, rough): 420 µm, 16.5 pt

(1 pt = 0.001 in = 25.4 µm. Arctic Paper supplies both Munken papers as laminated sheets at 300 gsm.)

The thickest is 84% thicker than the thinnest at the same gsm. This is why "300 gsm = 14 pt," a line found in at least one ranking guide, is not reliable. On these five papers, 300 gsm ranges from 9 to 16.5 pt.

Mills publish this as bulk: thickness in µm divided by gsm (the inverse of density). Higher bulk means a thicker sheet for the same weight. Munken Pure Rough has a bulk of 1.4. Magno Gloss is around 0.76. Gloss paper is pressed harder to get its shine, which makes it thinner.

A practical consequence: a 200 gsm Munken Pure sheet (226 µm) is about as thick as a 300 gsm Magno Gloss sheet (228 µm). If a thick feel is what you want, a bulkier uncoated paper gets you there at a lower weight. For how coating affects print quality, see our guide to coated paper.

If your printer quotes thickness, compare in µm or pt. If they only give gsm, ask which paper it is and check the mill's datasheet.

 

Which paper weight to use

• Letterheads and compliment slips: 90 to 120 gsm uncoated. Must run through office printers.
• Flyers: 130 to 170 gsm. Lighter paper lets more of the back show through: Magno Gloss is 90% opaque at 90 gsm and 96.5% at 150 gsm.
• Folded leaflets: 130 to 170 gsm. Heavier stock needs scoring (see below).
• Posters (indoor): 150 to 200 gsm
• Brochure inner pages: 115 to 170 gsm
• Brochure covers: 250 to 300 gsm
• Postcards: 300 to 350 gsm
• Business cards: 350 gsm or more. Check thickness too, since a 350 gsm gloss card can feel thinner than a 300 gsm uncoated one.

 

When heavier paper needs scoring

Thick paper cracks when folded, and on coated stock the crack shows as a white line through any printed color. Sappi's datasheets recommend pre-creasing (scoring) from 135 µm thickness.

Applying that 135 µm threshold to each paper's thickness data:

• Magno Gloss: score from 200 gsm (150 µm)
• Magno Satin: score from 170 gsm (141 µm)
• Magno Matt: score from 150 gsm (150 µm)
• Munken Pure: from 120 gsm (136 µm)
• Munken Pure Rough: from 100 gsm (140 µm)

The 135 µm figure is Sappi's recommendation for its own papers. We applied it to Munken for comparison, and uncoated paper generally cracks less visibly than coated because there is no coating layer to break. Still, a folded leaflet at 150 gsm might need scoring on one paper and not on another, which is a question to ask before printing, not after.

 

Before you order

1. Give the weight in gsm. If you order in lb, include the category (text or cover).
2. If thickness matters, ask for the paper name and look up its thickness in µm on the mill's datasheet.
3. For anything folded above 130 gsm, ask whether it will be scored.
4. Set up bleed in your file before sending. Our bleed in printing guide explains the standard sizes.

 

Sources

• Sappi, Magno Gloss datasheet 2025
• Sappi, Magno Satin datasheet 2025
• Sappi, Magno Matt datasheet 2025
• Arctic Paper, Munken Pure technical specification
• Arctic Paper, Munken Pure Rough technical specification
• Clearprint, GSM paper weight chart (catalogue equivalents)