Paper Weights Explained: GSM, Pounds and Which Paper to Use
Paper weight in the UK is given in grams per square metre (gsm or g/m²): the weight of one square metre of a single sheet. A higher gsm means a heavier, usually thicker paper, and gsm can be compared directly across every type of paper. US pound (lb) figures are different: they are the weight of a ream of 500 sheets at a basic size that changes with the paper grade, so an "80 lb" cover card and an "80 lb" text paper are not the same weight.
This guide explains gsm and lb, gives typical weights for printer paper, card, sketchbooks and watercolour paper, and covers watercolour surfaces and fibres.
How gsm works
Gsm is simple: cut a square metre of the paper and weigh it. Standard office paper is usually around 80 gsm, light card is roughly 160–220 gsm, and a standard watercolour paper is 300 gsm. Because the area is always one square metre, 300 gsm watercolour paper and 300 gsm card weigh the same per sheet of the same size, even though they feel different.
Gsm measures weight, not thickness. A dense, smooth paper and a soft, bulky paper of the same gsm can feel quite different in the hand, so use gsm as a guide alongside the description of the paper.
Why US pound weights are confusing
In the US system, basis weight is the weight in pounds of 500 sheets cut to a standard size, but that size depends on the grade. Valmet's table of ream sizes lists the main basic sizes and conversion factors:
| Grade | Basic sheet size | Multiply lb by (to get gsm) |
|---|---|---|
| Bond / writing | 17 × 22 in | 3.76 |
| Text / book / offset | 25 × 38 in | 1.48 |
| Cover | 20 × 26 in | 2.71 |
Watercolour paper uses yet another basis: a ream of 500 Imperial sheets of 22 × 30 in. Working that out gives roughly 2.13 gsm per lb, which is why 140 lb watercolour paper is about 300 gsm.
Some worked examples show why lb numbers cannot be compared across grades:
- 80 gsm office paper is about 21 lb bond, but about 54 lb text.
- "80 lb" text paper is about 118 gsm, while "80 lb" cover card is about 216–217 gsm.
- 300 gsm is about 110 lb if sold as cover card, but 140 lb if sold as watercolour paper.
If a pad lists both figures, go by the gsm. If it lists only pounds, check which grade it is before comparing.
Typical gsm by use
| Approx. gsm | Typical use | Notes |
|---|---|---|
| 70–100 | Printer and copier paper, practice sketching | 80 gsm is the everyday office standard |
| 90–150 | Sketchbooks and cartridge paper | Fine for pencil, pen and charcoal; buckles with heavy wet media |
| 150–250 | Mixed media pads, light card | Takes light washes, markers and ink |
| 200–300 | Cardstock for card making, die cutting and invitations | Check your printer's maximum gsm before printing on card |
| 190 | Lightweight watercolour paper | Affordable for practice; buckles noticeably when wet |
| 300 | Standard watercolour paper | The most common choice for pads and blocks |
| 425 | Heavier watercolour paper | Less cockling with wetter washes |
| 638–640 | Heaviest common watercolour paper | Stays much flatter; often used without stretching |
These are general ranges; manufacturers' own weights vary slightly. For home printing, your printer's manual lists the heaviest paper it can feed, and going over it can cause jams. Browse by use in our cardstock and sketchbooks categories.
Watercolour paper: weight, surface and fibre
Weights
The common watercolour weights are 190 gsm (90 lb), 300 gsm (140 lb), 425 gsm (200 lb) and 638 gsm (300 lb), often rounded to 640 gsm. St Cuthberts Mill, for example, lists its 100% cotton Saunders Waterford paper in weights from 190 gsm to 638 gsm (90 lb to 300 lb). Lighter sheets cockle (buckle) more when wet, which is why many painters stretch 190 and 300 gsm paper, or use gummed pads and blocks that are glued on all four sides, before heavy washes.
Hot-pressed, cold-pressed and rough
| Surface | Texture | Good for |
|---|---|---|
| Hot-pressed (HP) | Smooth | Fine detail, botanical work, pen and wash |
| Cold-pressed (CP, also called NOT) | Medium texture | The most versatile all-round surface |
| Rough | Pronounced texture | Landscapes, loose and expressive washes, granulation |
St Cuthberts Mill's advice on why watercolour paper matters describes HP as the smoothest surface for highly detailed work, CP as the most versatile and Rough as the most textured. "NOT" simply means not hot-pressed. Surface texture also varies between makers, so a cold-pressed sheet from one mill may feel smoother than another's.
Cotton or cellulose
- Cotton (often called 100% cotton or rag): strong when wet, absorbs evenly, copes with lifting, scrubbing and layering; usually the most expensive.
- Cellulose (wood pulp, sometimes alpha cellulose): more affordable and well suited to practice and studies; washes may dry faster and show hard edges sooner.
Many painters practise on cellulose paper and keep cotton for finished work. Both types are in our watercolour paper category. Our watercolour painting for beginners guide covers how to stretch paper and lay first washes.
Choosing paper for markers and mixed media
Gsm is only part of the story for other media. Alcohol markers can bleed through lighter papers, so makers often use dedicated marker paper or smooth card. Our guide to alcohol markers and water-based markers explains which papers suit each. For mixed media, look for a sized paper of around 200 gsm or more if you plan to add washes.
Quick summary
- Compare papers by gsm; it means the same for every grade.
- Treat lb figures with care: bond, text, cover and watercolour use different basic sizes.
- About 80 gsm for printing, 90–150 gsm for sketching, 200–300 gsm for card making.
- Watercolour: 190 gsm for practice, 300 gsm as the standard, 638–640 gsm for heavy washes.
- Choose HP for detail, CP/NOT for all-round painting, Rough for texture.
- Cotton for finished work, cellulose for practice and studies.
Frequently asked questions
What does gsm mean on paper?
Gsm stands for grams per square metre: the weight of one square metre of a single sheet. A higher gsm means a heavier paper, and it can be compared across all paper types.
What gsm is normal printer paper?
Everyday office and printer paper in the UK is usually around 80 gsm. Check your printer's manual before printing on heavier card, as each printer has a maximum weight.
Is 300 gsm the same as 140 lb?
For watercolour paper, yes: 300 gsm is roughly equivalent to 140 lb because watercolour pounds are based on 500 sheets of 22 × 30 in. Sold as cover card, 300 gsm would be about 110 lb.
Why are lb paper weights not comparable?
US pound weights measure 500 sheets at a basic size that depends on the grade, such as bond, text, cover or watercolour. So an 80 lb cover card is much heavier than an 80 lb text paper.
What is the difference between hot-pressed and cold-pressed watercolour paper?
Hot-pressed paper is smooth and suits fine detail, cold-pressed (NOT) has a medium texture and is the most versatile, and rough has the most texture. Texture also varies between makers.