Skip to content
ToolBoxGeniehome

GSM Converter

Converters · Added

GSM is a straightforward unit: grams of paper or cloth per square metre. US paper basis weights are not, because a basis weight is the weight of 500 sheets at that grade's parent size — and every grade has a different parent size. That is why 80 lb cover and 80 lb text are nearly two to one, and why this asks which grade before it converts anything.

What are you converting

Result

120 g/m² converted

3.53922296 oz/yd²

Light card as paper · Light as fabric

Grams per square metre
120

g/m², the international standard

Ounces per square yard
3.53922296

oz/yd², the US textile unit

Pounds per 1000 sq ft
24.5779372

packaging and board

120 g/m² as a basis weight in every grade

Bond / writing / ledger (17 × 22 in)
31.9 lb
Text / book / offset (25 × 38 in)
81.1 lb
Cover / card (20 × 26 in)
44.4 lb
Bristol (22.5 × 28.5 in)
54.7 lb
Index (25.5 × 30.5 in)
66.4 lb
Tag (24 × 36 in)
73.7 lb
Newsprint (24 × 36 in)
73.7 lb

This table is the whole reason the tool asks for a grade. The same paper is 80 lb in one grade and 30 lb in another, because a basis weight is 500 sheets of that grade's parent size — and every grade has a different parent size. "80 lb cover" and "80 lb text" are not close: one is roughly twice the weight of the other.

In every unit

Gram per square metre (g/m²)
120
Kilogram per square metre (kg/m²)
0.12
Milligram per square centimetre (mg/cm²)
12
Gram per square centimetre (g/cm²)
0.012
Ounce per square yard (oz/yd²)
3.53922296
Ounce per square foot (oz/ft²)
0.393246996
Pound per square yard (lb/yd²)
0.221201435
Pound per square foot (lb/ft²)
0.0245779372
Pound per 1000 square feet (lb/1000 ft²)
24.5779372

What that weight usually means

  • Paper — Light card. Brochure covers, folded leaflets that need to hold a crease.
  • Fabric — Light. Shirting, light jersey, poplin, quilting cotton.

Thickness cannot be computed from weight. Bulk varies by a factor of two between a coated gloss sheet and an uncoated bulky one at the same gsm, so caliper is always quoted separately on the datasheet.

Derived from the exact definitions: the pound is 453.59237 g, the yard 0.9144 m and the foot 0.3048 m. One ounce per square yard is 33.906 g/m², which is why a 5 oz/yd² jersey and a 170 gsm jersey are the same cloth.

How to use the gsm converter

  1. 1For fabric or metric paper, use the first mode: enter a weight and convert between g/m², oz/yd² and the rest.
  2. 2For US paper, switch to basis weight and pick the grade first — bond, text, cover, index, bristol, tag or newsprint.
  3. 3Enter the pounds, or a gsm figure to go the other way.
  4. 4Look at the comparison table: it shows what the same paper would be called in every other grade.

Examples

The confusion this exists for

Input
216 g/m² card
Result
80 lb as cover, but 146 lb as text and 57 lb as bond

Three different pound figures, one piece of card. The grade is not optional information.

Ordinary printer paper

Input
20 lb bond
Result
75 g/m²

The 80 gsm sold in most of the world is very slightly heavier than a US 20 lb ream.

A T-shirt

Input
5 oz/yd²
Result
169.5 g/m² — a mid-weight jersey

One ounce per square yard is 33.906 g/m², which is why 5 oz and 170 gsm shirts are the same thing.

About the gsm converter

Why the US basis weight system works the way it does

It is a survival from how paper was actually sold. Mills made and shipped paper in large parent sheets, and the price and the specification followed the weight of a ream of those sheets. Each type of paper had its own traditional parent size — bond at 17 × 22 inches because four letter sheets cut from it exactly, text at 25 × 38, cover at 20 × 26 — and the basis weight was simply the weight of 500 of them.

That made sense to a printer buying parent sheets and made no sense at all to anyone comparing across grades, which is most people now. The metric system sidestepped the whole problem by measuring the paper rather than the ream: grams per square metre is a property of the sheet, independent of what size anybody cuts it to. It is why the rest of the world converged on GSM and why cross-border print specifications are written in it.

What weight does and does not tell you

Weight predicts stiffness roughly, opacity roughly, and postage exactly. It is the right number for working out whether a mailing will cross a postal weight band, and for a first guess at whether a sheet will feel flimsy.

It predicts almost nothing else. Opacity depends heavily on fillers and coating, so a well-filled 90 gsm sheet can show less show-through than a cheap 100 gsm one. Stiffness depends on bulk as much as mass. Print quality depends on the surface. And in fabric the weight is barely half the story: fibre content, weave structure and finish decide how a cloth behaves, which is why a specification that gives only a gsm figure has not really specified anything.

Frequently asked questions

Why is 80 lb cover heavier than 80 lb text?
Because a basis weight is the weight of 500 sheets of that grade's parent size, and the parent sizes differ. Text is 25 × 38 inches, cover is 20 × 26. A ream of cover is spread over far less area for the same total weight, so each sheet is much heavier: 80 lb cover is 216 g/m² while 80 lb text is 118 g/m². The pound figure is meaningless without the grade attached, which is the single most common misunderstanding in ordering paper.
How is the conversion actually calculated?
Directly from the definition rather than from a chart. The areal density is the ream weight divided by the ream area: pounds times 453.59237 grams, divided by 500 sheets times the parent width times the height in square inches, converted into square metres. Folding the constants gives a single multiplier per grade — 1.4801 for text, 2.7041 for cover, 3.7597 for bond — and every figure this tool reports comes out of that arithmetic.
Can I get the thickness from the weight?
No, and any tool that offers to has assumed a density without telling you. Thickness depends on bulk, which is a property of the pulp, the coating and how hard the sheet was calendered. Two papers at the same gsm can differ in caliper by a factor of two — a coated gloss sheet is dense and thin, while an uncoated bulky book paper of the same weight is noticeably thicker, which is exactly why publishers specify it. Caliper is quoted separately on every datasheet for this reason.
What gsm should I use for a business card or a flyer?
As orientation rather than a rule: flyers and brochure pages sit around 130 to 170 gsm, folded leaflets that need to hold a crease around 170 to 250, and business cards from 300 gsm upward — 350 and 400 gsm are common for cards that feel substantial. Ordinary office paper is 80 gsm. Any printer will have their own stocked ranges, and the finish changes how a given weight feels in the hand as much as the number does.
Does the same scale mean the same thing for fabric?
The unit is identical — grams per square metre — but the descriptive bands are completely different, because fabric at 170 gsm is a T-shirt while paper at 170 gsm is card. The other difference is that fabric weight tells you much less: fibre, weave and finish change how a cloth drapes, wears and feels far more than a weight figure does. Two 300 gsm fabrics can be a stiff canvas and a soft brushed fleece.

Related tools