Comment by Fiveplus
2 days ago
Nice! The author touches on the area properties and here's the most practical life hack derived from the standard I personally use. It uses the relationship between size and mass.
Because A0 is defined as having an area of exactly 1 square meter, the paper density (GSM or grams per square meter) maps directly to the weight of the sheet.
>A0 = 1 meter square.
>Standard office paper = 80 gsm
>Therefore, one sheet of A0 = 80 grams.
>Since A4 is 1/16th of an A0, a single sheet of standard A4 paper weighs 5 grams.
I rarely need to use a scale for postage. If I have a standard envelope (~5g) and 3 sheets of paper (15g), I know I'm at 20g total. It turns physical shipping logistics into simple integer arithmetic. The elegance of the metric system is that it makes the properties of materials discoverable through their definitions.
The 5 grams per sheet of common printer paper has certainly proven handy once or twice in some of my interactions in the informal economy.
Same for the US 5 cent coin. Defined mass of 5 grams.
Don't tell the current administration that there's something so un-American about the currency: they will insist on fixing it, and probably retire Jefferson as well.
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And $20 in dimes or quarters is 1 lb. US silver coins are 0.2268 grams per cent.
Paper's uniform mass per area makes it useful calibrating very tiny scales. 1mm² of 80 gsm paper will weigh about 80 micrograms.
"Measure the mass of an eyelash with a DIY microbalance" by Applied Science https://youtu.be/ta7nlkI5K5g
TIL GSM is just g/sq m. Like duh, feel so stupid xD
It's not you who should feel stupid.
The person deciding to use nonstandard "GSM" as a unit instead of the proper "g/m²" needs to feel stupid...
I'm not sure I agree. "GSM" is three syllables, versus four for "grammes per square metre". You can write it correctly using only characters everyone knows how to type quickly on their keyboard, versus either finding a way to get that superscript ² or else typing something like g/m^2 which is uglier and longer. And you can use it comfortably even if you are a complete mathematical ignoramus (you just need to know things like "larger numbers mean heavier paper" and "cheap printer paper is about 80gsm" and so forth) without the risk of turning g/m² into the nonsensical g/m2 or something.
(But arguably what whoever decided on "gsm" should have done was to just use "g", with the "per square metre" left implicit.)
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"The person deciding to use nonstandard "GSM" as a unit instead of the proper "g/m²" needs to feel stupid..." ---> This is the sort of HN comment that I can't figure out if it's serious or a joke. I can read it in different voices and come to opposite conclusions haha
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You mean gm⁻² ?
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Some cursory search suggests "gsm" for grammature is confined to the US, everyone else uses g/m² or just g.
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Ummm, not really, No.
The shorthand "gsm" is a completely standard alternative in some industries.
I work in advanced composites. Different weights and weaves of technical fabrics such as carbon fiber, kevlar, fiberglass, etc. are always specified in "gsm". For example, some common fabrics would be a "Carbon Fiber 3K 200gsm Twill" or a "High Modulus 12K 380gsm Carbon Fiber Plain Weave". (the "3K" and "12K" refer to the number of carbon fiber strands in each yarn in the weave, and the "Twill" and "Plain Weave" refer to the pattern in which the yarns are woven into a fabric.)
I'm sure "gsm" came to be commonly used instead of the more scientific "g/m²" or "g/m^2" because no one is doing that kind of math about the materials, and it is a lot easier to type "gsm" vs either of the other two which require at least a Shift for the caret or getting out the superscript font attribute.
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> The person deciding to use nonstandard "GSM" as a unit instead of the proper "g/m²" needs to feel stupid...
mph, kph, cps, etc
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Oh nice, that is a neat trick! One small nitpick (that makes no difference): The side lengths of the ISO Ax formats are rounded to the next mm, so actually the A0-format has an area of 0.999949m^2
Not to the next, to the nearest, otherwise it would have to be slightly larger than 1m^2.
that reminds me of an old joke: how doe the postal services make their profit? I don't get it. - Ah, that's easy. How much wieght may letters have? - 20g - And how much weight do the average letters have? - About 6g. - See? That's their profit
I really don't get it.
It's technically a 300% margin because they are charging you for 20g but only shipping 6g.
> I rarely need to use a scale for postage. If I have a standard envelope (~5g) and 3 sheets of paper (15g), I know I'm at 20g total. It turns physical shipping logistics into simple integer arithmetic.
...was using a scale for postage a concern? If you're shipping things on the order of three sheets of paper, you're way below any conceivable threshold. USPS charges a flat rate on letters under 370 grams!
If you're sending 1,700 pieces of looseleaf paper in a box... just weigh the box.
German postage for letters is under 20g, under 50g and under 500g so I had this issue a few times so far when sending a few letters a day over a few weeks. You can see it here for international letters for example: https://www.deutschepost.de/en/b/briefe-ins-ausland.html
Thankfully I just had a scale, but I can see this being helpful when you don't.
Given that we are talking about A4 papers and grams, I'd bet this wasn't in the US.
In Europe, the typical flat rate is up to 100g for standard letters. And that's 20 sheets, which is not a particularly unusual letter to send.
But 20 sheets do not fit in a regular DL or C5 envelope so you already have an hint that you may check the limits, you usually send them in a reinforced C4 enveloppe.
French "La Poste" sets the first threashold at 20 g.
You will be using Aerograms soon.
https://en.wikipedia.org/wiki/Aerogram
On a related subject I just discovered that sending a letter in Denmark now costs a minimum of $4.50.
>USPS charges a flat rate on letters under 370 grams!
In the UK the limit for a letter is 100 grams:
https://www.royalmail.com/sending/uk/1st-class
And as that link eventually shows there are limits on the dimensions as well. I sometimes think a simple table might be better than these interactive pages, but I suppose it has to work on a phone.
24 by 16.5 by 0.5 cm for the standard 1st class letter. So you could send an A5 booklet made of less than 20 sheets of A4 (80 g/m^2) paper as a standard letter.
If the postage is short, our lovely privatised Post Office holds the letter and makes the recipient pay the excess.
Back on thread: Repeatedly fold an A0 sheet of paper in half. How many folds can you do? A ream (500 sheets) of 80 g/m^2 paper is about 2.5cm thick. (good when teaching geometric progressions).
In Sweden, the lowest postage (one stamp, 22 SEK or around $2) is for max 50 grams.
A first class forever stamp only covers 1oz (28g).