Units of measurement vary across different countries. For example, mass can be measured in kilograms or pounds; temperature in degrees Celsius or Fahrenheit; distances in kilometers or miles, centimeters or inches; volumes in liters or gallons, etc. In Japan, mass is measured in kilograms, but when it comes to paper, its mass is not calculated in grams per square meter but in kilograms.
Example: In France, we have paper that can be, among other things, 90 g/m², 120 g/m², etc.In Japan, we have paper that can be, for example, 110 kg, 135 kg, etc.
Where it’s simple in France is that you immediately know the exact weight of the paper, with so many grams for a 1 m² sheet. And where it gets a bit more complicated in Japan is that you don’t know what measurements or volume the kilograms correspond to unless you ask the question. That’s what I’m going to explain here. Finally, I could summarize this in two lines, but I’ll also explain other things related to paper. It’s for your general knowledge.
To begin with, in Japan, when paper is manufactured at the factory, it is produced in two large basic formats: the kikuban 菊判 (636×939mm) for A sizes and the shirokuban 四六判 (788×1,091mm) for B sizes. These serve as the basis for all JIS-standard paper formats, such as A4, which is always 210x297mm, and B4, which is always 257x364mm, for example. As you might have guessed, kikuban paper is used to produce sheets in formats A1, A2, A3, A4, A5, and A6. As for shirokuban paper, it is used to produce sheets in formats B1, B2, B3, B4, B5, B6, L-ban, and hatoron-ban.
For example, if you want to print an A4-sized magazine, you would use kikuban paper, which will yield eight sheets per sheet, or sixteen pages of a magazine (since paper is printed on both sides for magazines, newspapers, books, etc.).
As I also mentioned manga genkou youshi, we know that the size used for publication is B4 according to JIS standards, or 257×364mm. It is obtained from a sheet of shirokuban (788x1,091mm) that has been cut into eight pieces. So, from one shirokuban sheet, you get a total of eight B4-sized manga genkou youshi sheets.
If you have fun calculating, you’ll notice that the cut formats do not exactly match the final format of a magazine, for example. This is because there is paper waste that is used for bleed areas.
Now, to get back to the paper weight, it's much simpler. The weight indicated on your pack of paper corresponds to one thousand sheets of shirokuban format if it's B-sized paper, or one thousand sheets of kikuban format if it's A-sized paper.
So, our manga genkou youshi of 110 kg corresponds to the weight of one thousand sheets of 788x1,091mm. It's as simple as that.
Mass and Thickness of Paper
Shirokuban (788mm × 1091mm, weight of a thousand sheets) → Practical thickness (thickness) mm / μ- 45kg approx. → approx. 0.06mm / approx. 60μ
- 55kg approx. → approx. 0.07mm / approx. 70μ
- 68kg approx. → approx. 0.09mm / approx. 90μ
- 73kg approx. → approx. 0.10mm / approx. 100μ
- 90kg approx. → approx. 0.12mm / approx. 120μ
- 110kg approx. → approx. 0.15mm / approx. 150μ
- 135kg approx. → approx. 0.18mm / approx. 180μ
- 160kg approx. → approx. 0.21mm / approx. 210μ
- 180kg approx. → approx. 0.24mm / approx. 240μ
And how much is that per square meter?
Well, you just need to do the math, but I’ll do it for you.
For Shirokuban paper (in B sizes), here’s what you might encounter:
- 135kg → 157.0g/m²
- 110kg → 127.9g/m²
- 90kg → 104.7g/m²
- 73kg → 84.9g/m²
- 70kg → 81.5g/m²
- 68kg → 79.1g/m²
- 63kg → 73.3g/m²
- 55kg → 64.0g/m²
- 45kg → 52.3g/m²
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