Basis weight of paper
Encyclopedia
The paper density of a type of paper
or cardboard is the mass
of the product per unit of area
. The term density here is not used in its traditional sense
of mass
per unit volume
. "Paper density", rather, is a measure of the area density. Paper products that let little or no light pass through (e.g. poster board) are considered dense or heavy. Paper products that allow some light to pass through (e.g. tissue paper) are considered lightweight.
Two ways of expressing paper density are commonly used:
, the density of all types of paper and paperboard is expressed in terms of grams per square metre (g/m²). This quantity is commonly called grammage in both English
and French
(ISO 536), though printers in most English-speaking countries still refer to the "weight
" of paper.
Typical office paper has 80 g/m², therefore a typical A4 sheet ( m²) weighs 5 g.
The unofficial unit symbol "gsm" instead of the standard "g/m²" is also widely encountered in English speaking countries.
While paper is measured by weight, card is measured by thickness in micrometres.
Typically grammage is measured in paper mill on-line by Quality Control System (QCS)
and verified by laboratory measurement.
In countries that use United States paper size
s, a less direct measure known as basis weight is used in addition to or instead of grammage. The basis weight of paper is the density of the number of sheets in that ream, and the dimensions of an "uncut" sheet in that ream.
The standard dimensions and sheet count of a ream vary according to the type of paper. These "uncut" basis sizes are not normally labelled on the product, are not formally standardized, and therefore have to be guessed or inferred somehow from trading practice. Historically, this convention is the product of pragmatic considerations such as the size of a sheet mold.
By using the same basis sheet size for the same type of paper, consumers can easily compare papers of differing brands. Twenty pound bond paper is always lighter and thinner than 32 pound bond, no matter what its cut size. And 20 pound bond letter size and 20 pound bond legal size papers are the same weight paper having different cut size.
However, a sheet of common copy paper that has a basis weight of 20 pounds (9.1 kg) does not have the same mass as the same size sheet of coarse paper (newsprint). In the former case, the standard ream is 500 sheets of 17 by paper, and in the latter, 500 sheets of 24 by paper. Here are some basic ream sizes for various types of paper. Units are inches except where noted.
Sheets 17 by can be cut into four 8.5 by sheets, a standard for business stationery known conventionally as letter sized paper. So, the 17 by ream became commonly used. The 25 by book-paper ream developed because such a size can easily be cut into sixteen 6 by 9 inches (229 mm) book-sized sheets without significant waste.
Early newsprint presses printed sheets 2 by in size, and so the ream dimensions for newsprint became 24 by, with 500 sheets to a ream. Newsprint was made from ground wood pulp, and ground wood hanging paper (wallpaper
) was made on newsprint machines. Newsprint was used as wrapping paper, and the first paper bags were made from newsprint. The newsprint ream standard also became the standard for packaging papers, even though in packaging papers kraft pulp rather than ground wood was used for greater strength.
Paper weight is sometimes stated using the "#
" symbol. For example, "20#" means "20 pounds per basis ream of 500 sheets".
When the density of a ream of paper is given in pounds, it is often accompanied by its "M weight". The M weight is the weight (in pounds) of 1000 cut sheets. Paper suppliers will often charge by M weight, since it is always consistent within a specific paper size, and because it allows a simple weight calculation for shipping charges.
For example, a 500-sheet ream of 20# 8.5 bycopy paper may be specified "10 M". 1000 cut sheets (or two reams) will weigh 10 lb (4.5 kg), half of the four reams of cut paper resulting from the 20# basis ream of 17 by paper.
is typically not directly known or specified, the thickness of any sheet of paper cannot be calculated by any method. Instead, it is measured and specified separately as its caliper
. However, paper thickness for most typical business papers might be similar across comparable brands. If thickness is not specified for a paper in question, it must be either measured or guessed based on a comparable paper's specification.
Caliper is usually measured in micrometres (1/1000 of a mm), or in the United States also in mils. (1 mil = 0.001 inch = 25.4 µm)
Typically grammage is measured in paper mill on-line by Quality Control System (QCS)
and verified by laboratory measurement.
Paper
Paper is a thin material mainly used for writing upon, printing upon, drawing or for packaging. It is produced by pressing together moist fibers, typically cellulose pulp derived from wood, rags or grasses, and drying them into flexible sheets....
or cardboard is the mass
Mass
Mass can be defined as a quantitive measure of the resistance an object has to change in its velocity.In physics, mass commonly refers to any of the following three properties of matter, which have been shown experimentally to be equivalent:...
of the product per unit of area
Area
Area is a quantity that expresses the extent of a two-dimensional surface or shape in the plane. Area can be understood as the amount of material with a given thickness that would be necessary to fashion a model of the shape, or the amount of paint necessary to cover the surface with a single coat...
. The term density here is not used in its traditional sense
Density
The mass density or density of a material is defined as its mass per unit volume. The symbol most often used for density is ρ . In some cases , density is also defined as its weight per unit volume; although, this quantity is more properly called specific weight...
of mass
Mass
Mass can be defined as a quantitive measure of the resistance an object has to change in its velocity.In physics, mass commonly refers to any of the following three properties of matter, which have been shown experimentally to be equivalent:...
per unit volume
Volume
Volume is the quantity of three-dimensional space enclosed by some closed boundary, for example, the space that a substance or shape occupies or contains....
. "Paper density", rather, is a measure of the area density. Paper products that let little or no light pass through (e.g. poster board) are considered dense or heavy. Paper products that allow some light to pass through (e.g. tissue paper) are considered lightweight.
Two ways of expressing paper density are commonly used:
- Expressed in grams per square metre (g/m²), paper density is also known as grammage. This is the measure used in most parts of the world.
- Expressed in terms of the mass (expressed as weight) per number of sheets, it is known as basis weight. The convention used in the United States and a few other countries using US paper sizePaper sizeMany paper size standards conventions have existed at different times and in different countries. Today there is one widespread international ISO standard and a localised standard used in North America . The paper sizes affect writing paper, stationery, cards, and some printed documents...
s is pounds of a ream of 500 (or in some cases 1000) sheets of a given (raw, still uncut) basis size. Japanese paper is expressed as the weight in kg of 1000 sheets.
Grammage
In the metric systemMetric system
The metric system is an international decimalised system of measurement. France was first to adopt a metric system, in 1799, and a metric system is now the official system of measurement, used in almost every country in the world...
, the density of all types of paper and paperboard is expressed in terms of grams per square metre (g/m²). This quantity is commonly called grammage in both English
English language
English is a West Germanic language that arose in the Anglo-Saxon kingdoms of England and spread into what was to become south-east Scotland under the influence of the Anglian medieval kingdom of Northumbria...
and French
French language
French is a Romance language spoken as a first language in France, the Romandy region in Switzerland, Wallonia and Brussels in Belgium, Monaco, the regions of Quebec and Acadia in Canada, and by various communities elsewhere. Second-language speakers of French are distributed throughout many parts...
(ISO 536), though printers in most English-speaking countries still refer to the "weight
Weight
In science and engineering, the weight of an object is the force on the object due to gravity. Its magnitude , often denoted by an italic letter W, is the product of the mass m of the object and the magnitude of the local gravitational acceleration g; thus:...
" of paper.
Typical office paper has 80 g/m², therefore a typical A4 sheet ( m²) weighs 5 g.
The unofficial unit symbol "gsm" instead of the standard "g/m²" is also widely encountered in English speaking countries.
While paper is measured by weight, card is measured by thickness in micrometres.
Typically grammage is measured in paper mill on-line by Quality Control System (QCS)
Quality Control System QCS for paper, board and tissue machines
A quality control system refers to a system used to measure and control the quality of moving sheet processes on-line; e.g. the paper produced by a paper machine. Generally, a control system is concerned with measurement and control of one or multiple properties in time;i.e. in a single dimension...
and verified by laboratory measurement.
In countries that use United States paper size
Paper size
Many paper size standards conventions have existed at different times and in different countries. Today there is one widespread international ISO standard and a localised standard used in North America . The paper sizes affect writing paper, stationery, cards, and some printed documents...
s, a less direct measure known as basis weight is used in addition to or instead of grammage. The basis weight of paper is the density of the number of sheets in that ream, and the dimensions of an "uncut" sheet in that ream.
The standard dimensions and sheet count of a ream vary according to the type of paper. These "uncut" basis sizes are not normally labelled on the product, are not formally standardized, and therefore have to be guessed or inferred somehow from trading practice. Historically, this convention is the product of pragmatic considerations such as the size of a sheet mold.
By using the same basis sheet size for the same type of paper, consumers can easily compare papers of differing brands. Twenty pound bond paper is always lighter and thinner than 32 pound bond, no matter what its cut size. And 20 pound bond letter size and 20 pound bond legal size papers are the same weight paper having different cut size.
However, a sheet of common copy paper that has a basis weight of 20 pounds (9.1 kg) does not have the same mass as the same size sheet of coarse paper (newsprint). In the former case, the standard ream is 500 sheets of 17 by paper, and in the latter, 500 sheets of 24 by paper. Here are some basic ream sizes for various types of paper. Units are inches except where noted.
| Paper Type | Paper Size Paper size Many paper size standards conventions have existed at different times and in different countries. Today there is one widespread international ISO standard and a localised standard used in North America . The paper sizes affect writing paper, stationery, cards, and some printed documents... |
- Number of sheets | |
| Bond, writing, ledger | 17 | × 22 | |
| Manuscript cover | 18 | × 31 | |
| Blotting | 19 | × 24 | |
| Box cover | 20 | × 24 | |
| Cover | 20 | × 26 | |
| Bristol and tag | 22½ | × 28½ | |
| Tissue | 24 | × 36 | |
| Newsprint | 24 | × 36 | |
| Hanging, waxing, bag, etc. | 24 | × 36 | |
| Book, Text, Offset | 25 | × 38 | |
| Index bristol | 25½ | × 30½ | |
| Paperboard (all types) | 12 | × 12 | |
Sheets 17 by can be cut into four 8.5 by sheets, a standard for business stationery known conventionally as letter sized paper. So, the 17 by ream became commonly used. The 25 by book-paper ream developed because such a size can easily be cut into sixteen 6 by 9 inches (229 mm) book-sized sheets without significant waste.
Early newsprint presses printed sheets 2 by in size, and so the ream dimensions for newsprint became 24 by, with 500 sheets to a ream. Newsprint was made from ground wood pulp, and ground wood hanging paper (wallpaper
Wallpaper
Wallpaper is a kind of material used to cover and decorate the interior walls of homes, offices, and other buildings; it is one aspect of interior decoration. It is usually sold in rolls and is put onto a wall using wallpaper paste...
) was made on newsprint machines. Newsprint was used as wrapping paper, and the first paper bags were made from newsprint. The newsprint ream standard also became the standard for packaging papers, even though in packaging papers kraft pulp rather than ground wood was used for greater strength.
Paper weight is sometimes stated using the "#
Number sign
Number sign is a name for the symbol #, which is used for a variety of purposes including, in some countries, the designation of a number...
" symbol. For example, "20#" means "20 pounds per basis ream of 500 sheets".
When the density of a ream of paper is given in pounds, it is often accompanied by its "M weight". The M weight is the weight (in pounds) of 1000 cut sheets. Paper suppliers will often charge by M weight, since it is always consistent within a specific paper size, and because it allows a simple weight calculation for shipping charges.
For example, a 500-sheet ream of 20# 8.5 bycopy paper may be specified "10 M". 1000 cut sheets (or two reams) will weigh 10 lb (4.5 kg), half of the four reams of cut paper resulting from the 20# basis ream of 17 by paper.
Conversions
The following chart shows standard conversions for bond/writing/ledger size paper (17" x 22"). These are a guide only, and are not necessarily always accurate.| Basis Weight (lb) |
Caliper (inches) |
Thickness (mm) |
Grammage (g/m²) |
|---|---|---|---|
| 16 | .0032 | 0.081 | 60.20 |
| 18 | .0036 | 0.092 | 67.72 |
| 20 | .0038 | 0.097 | 75.20 |
| 24 | .0048 | 0.120 | 90.30 |
| 28 | .0058 | 0.147 | 105.35 |
| 29 | .0060 | 0.152 | 109.11 |
| 31 | .0061 | 0.155 | 116.63 |
| 35 | .0062 | 0.157 | 131.68 |
| 36 | .0068 | 0.173 | 135.45 |
| 39 | .0072 | 0.183 | 146.73 |
| 40 | .0073 | 0.185 | 150.50 |
| 43 | .0074 | 0.188 | 161.78 |
| 44 | .0076 | 0.193 | 165.55 |
| 47 | .0078 | 0.198 | 176.83 |
| 53 | .0085 | 0.216 | 199.41 |
| 54 | .009 | 0.229 | 203.17 |
| 58 | .0092 | 0.234 | 218.22 |
| 65 | .0095 | 0.241 | 244.56 |
| 67 | .010 | 0.250 | 252.08 |
| 72 | .011 | 0.289 | 270.90 |
| 76 | .013 | 0.330 | 285.95 |
| 82 | .014 | 0.356 | 308.52 |
| 87 | .015 | 0.380 | 312.00 |
| 105 | .0175 | 0.445 | 385.06 |
Caliper
Paper thickness, or caliper, is a common measurement specified and required for certain printing applications. Since a paper's densityDensity
The mass density or density of a material is defined as its mass per unit volume. The symbol most often used for density is ρ . In some cases , density is also defined as its weight per unit volume; although, this quantity is more properly called specific weight...
is typically not directly known or specified, the thickness of any sheet of paper cannot be calculated by any method. Instead, it is measured and specified separately as its caliper
Caliper
A caliper is a device used to measure the distance between two opposing sides of an object. A caliper can be as simple as a compass with inward or outward-facing points...
. However, paper thickness for most typical business papers might be similar across comparable brands. If thickness is not specified for a paper in question, it must be either measured or guessed based on a comparable paper's specification.
Caliper is usually measured in micrometres (1/1000 of a mm), or in the United States also in mils. (1 mil = 0.001 inch = 25.4 µm)
Typically grammage is measured in paper mill on-line by Quality Control System (QCS)
Quality Control System QCS for paper, board and tissue machines
A quality control system refers to a system used to measure and control the quality of moving sheet processes on-line; e.g. the paper produced by a paper machine. Generally, a control system is concerned with measurement and control of one or multiple properties in time;i.e. in a single dimension...
and verified by laboratory measurement.
See also
- Book sizeBook sizeThe size of a book is generally measured by the height against the width of a leaf, or sometimes the height and width of its cover. A series of terms is commonly used by libraries and publishers for the general sizes of modern books, ranging from "folio" , to "quarto" and "octavo"...
- Envelope size
- Hole punchHole punchA hole punch is a common office tool that is used to create holes in sheets of paper, often for the purpose of collecting the sheets in a binder or folder.The origins of the hole punch date back to Germany via Matthias Theel, where two early patents for a...
— filing holes - Index cardIndex cardAn index card consists of heavy paper stock cut to a standard size, used for recording and storing small amounts of discrete data. It was invented by Carl Linnaeus, around 1760....
- Paper and ink testingPaper and ink testingA variety of tests are used to determine ink and paper quality, and to measure their interactions. They are necessary to balance print quality, cost, and wear on the press.-List of paper and ink tests:Some of the paper and ink tests are listed here:...
- Paper sizePaper sizeMany paper size standards conventions have existed at different times and in different countries. Today there is one widespread international ISO standard and a localised standard used in North America . The paper sizes affect writing paper, stationery, cards, and some printed documents...
- Photographic printingPhotographic printingPhotographic printing is the process of producing a final image on paper for viewing, using chemically sensitized paper. The paper is exposed to a photographic negative, a positive transparency , or a digital image file projected using an enlarger or digital exposure unit such as a LightJet printer...
— standard photographic print sizes
External links
- Paper Weight - Conversion Chart
- Understanding Paper Weights
- Understanding paper weight (Staples, Inc.Staples, Inc.Staples Inc. is a large office supply chain store, with over 2,000 stores worldwide in 26 countries. Based in Framingham, Massachusetts, United States, the company has retail stores, serving customers under its original name in Austria, Brazil, China, France, Germany, India, Italy, Norway,...
) - M-weight Calculator
- Paper Weight Calculator