# Why are grams so small?

Consider the three basic metric units for measuring physical objects:

The metre
The litre
The gram

Out of the three of them, the first two are moderately (though not extraordinarily) large compared to what they replaced. The metre is basically a replacement for the foot - it’s three times as big. No problem. The litre replaces the pint - twice as big.

By comparison, the gram is tiny. In fact, it’s so tiny that in the sort of situations where one would use metres and litres for measuring length and volume, the gram is generally not used - the “standard” is a unit a thousand times as big, the kilogram.

Even more bizarrely, there was a prior weight unit, the “grave” which was, in fact, a thousand times bigger than a gram

So when they decided to change the name of the standard weight unit, why also shrink it a thousand times? Grams are too tiny to be sensibly used in basically any everyday application. So why wasn’t the thing named “gram”, defined to be kilogram-sized?

A meter is about a yard.

Yeah, but people use feet more often than yards, don’t they?

And the point still stands - metres are biggish, grams are tiny. A person, for instance is usually lsee than two of these “metres” - but many many thousand grams.

Actually, the base unit of mass in the international system is the kilogram, not the gram.

What people use the most doesn’t matter. A yard is the closest unit to a meter that we commonly use. Take it for what it was a friendly correction, not a bust your balls moment.

The problem was that the basic metric units were originally based on the properties of the earth (one metre was 1/10,000,000 of the distance from the North Pole to the Equator) and the properties of water. A gram was originally defined as the weight of a cubic centimetre of water, which isn’t much. Of course this only raises another question - why a cubic centimetre, not a cubic metre? Well that would have made the unit a million times heavier, which would still have been impracticable (1000 kg in our units). The fact is, the dimensions of the Earth and the weight of water are unrelated quantities which don’t necessarily give rise to human-sized units.

You seem to be working in circles.

It’s not that those things are approximately the same size as what they replaced, it is that you consider them a replacement because they are the same size. A litre didn’t replace a pint any more than than it replaced a fluid ounce or a barrel. A metre didn’t replace a foot any more than it replaced a mile or an inch. An a gram didn’t replace a pound any more than it replaced a hunderedweight.

You might just as well ask why a metre is so terribly much shorter than the mile that it replaced, or why a litre is so terribly much larger than a fluid ounce. Of course you don’t think that way because when you want a “replacement” for a mile you multiply it by a thousand and call it a kilometre, and when you want a replacement for a fluid ounce you automatically divide by a thousand and call it a milligram.

So when you want a replacement for a pound you should simply multiply by a thousand and call it a kilogram. It’s no different.

A kilogram is not standard anywhere in the metric world. Nowhere on three continents have I seen shops commonly selling goods by the kilogram. Very few things that you buy weigh more than kilogram so it would be stupid to try using that as the standard.

They didn’t. A gram is the mass of 1 cubic centimetre of water. It has never shrunk from that. If you are asking why they didn’t use the mass of one cubic metre, well you should be able to work that out for yourself once you realise that one cubic metre of water is a tonne.

Billions of people every day use grams in basically every single everyday application. The idea of buying loaves of bread or cans of beans weighed in tenths of a kilogram is just silly. the idea of buying condimenst weighed as thousandths of a gram is ludicrous. Not that the kilogram isn’t a perfectly usable unit, it just that it lacks precision for the vast majority of everyday tasks.

A better question is why you think it should have been? A gram is a very approximate replacement for an ounce sized unit, not for a pound sized unit. Defining it as kilogram size would require that 9/10 of the applications for the weight unit would require working in fractions. After all how much of your shopping has the weight marked in fractions of pounds?

True, but not much of an answer. Why is kilogram a base unit, but not kilometer nor kiloliter?

My WAG is that the everyday convenient uses of mass, length, and volume can be represented by the smallest round numbers using the existing standards. If for example they had called the kilogram standard a gram, then most chemists would find themselves dealing with the 6 decimal places of micrograms (what we know as milligrams) on a tiresomely regular basis. Yes, it’s just numbers, and nowadays with our fancy electronic computers we don’t think twice about the drudgery of computation, but that luxury didn’t exist back then.

You may be on to something here. Maybe there were a lot of chemists on the deciding committee?

You don’t ever buy apples? Potatoes? Seriously, I’ve never seen an item priced by the gram - even if you’re intending to buy less than a kilo of it it’s still priced by the kilogram - the kilogram is standard.

Furthermore, even when you want something in small quantities, you go by chunks of 10 or (more likely) 100 grams. I don’t ask for “187 g of sliced ham please” - I say “about 200g”. I’m thinking in chunks of 100 because the precision of the gram is too small to be actually useful.

You cannot be serious. Where on earth do you live? Almost everywhere in the world food and produce is sold in Kg. In China, the prices are quoted in 1/2 Kg which is closer to their traditional unit, but the computers are programmed and your ticket is printed by the kilogram.

The Kg is the standard unit of weight used around the world for almost everything and when you get into very high numbers it goes to the metric ton which is 1000 Kg.

You clearly don’t buy many class-A drugs.

No, they’d just use nanograms or picograms. I love metric.

It is the answer. The OP was incorrect in identifying the gram as the base unit of measure and based the rest of the post on that.

OK, I’ll grant you that fruit and meat are labelled by the kilo, although meat is actually sold by the gram. But that’s very much the exception. Check your last grocery receipt and unless you are living on fresh produce you’ll find that the vast majority is labelled and sold by the gram. Everything from bread and breakfast cereal through to cheese and down to the condiments. The same goes for most non-grocery products that you buy.

Yesss. I’m not sure what your point is here. No matter what your unit is, you have to round. If we followed your suggestion and worked in a kg equivalent weight you’d still be rounding, only you’d be working in chunks of tenths. You wouldn’t actually buy one kg when you wanted 150 grams would you? Surely you’d still be rounding only you’d be doing it in fractions rather than multiples. And then you;d presumably be wondering why the unit was so big compared to the ounce that it “replaced”.

Which simply demonstrates that the the kg is no more usable for everyday purposes than the gram.

Well Australia at the moment, but the EU, South Am and Africa are the same: the standard unit is the gram. Here is some fairly typical Brazilian food for example, and here are some German. As you can see, aside from a couple of “jumbo” items that happen to weigh exactly 1kg, it is all sold by the gram.

Perhaps you could name some of these countries where the typical unit for food and produce is the kilo, because I’ve never heard of them. Bonus points if you can produce some evidence for this claim. I find it extraordinary that there is a country that actually sells Cornflakes, for example in boxes of 0.2 kg rather than 200grams. Or staples in boxes of 0.05kg. It will be interesting to see boxes a labelled that way rather than in grams as I’ve seen everywhere else.

OK… as has already been corrected, the base unit is in fact the kilogram. To address the implied question of why is the mass unit the only one that has a prefix, this is the answer according to Wikipedia:

A little different from what I said, though I still maintain that the existing scale is much more convenient for everyday scientific calculations using pencil and paper. Yes, you could just use picograms or micrograms, but if you were using mixed units the extra decimal places would quickly become tiresome.

I know I’m not the first to pick up on this, but seriously… WTF?

You’re from the UK aren’t you? Most things sold by weight here are sold by the kg - or at least most things where a typical purchased measure weighs in at hundreds of grammes or more.

My cite is the first thing that came to hand: a pack of Cheddar cheese* - priced in £ per kg (with £ per lb included for the convenience of folks who still think in old money)

It’s not unusual for items such as this to bear a nett weight declaration of ‘910g’ instead of 0.910kg as seen here, but even in those cases, the offer price is most often expressed in £/kg

[sub]*Yes, I did put cheese on my scanner today.[/sub]

All you need to do is go to your local Chinese grocery; you’ll find stacks of rice in 1, 5, and 10kg bags. I’m not saying it’s the standard but it’s extremely common wherever foodstuffs are commonly sold in bulk.

Absolutely incorrect. The kilogram is the base unit for mass in the SI system. The standard kilogram is a cylinder made of a platinum-iridium alloy and is stored in a vault in Sèvres, France.

Today, a gram is defined as being 1/1000 the mass of the standard kilogram.

While a gram was once defined as the mass of a cubic centimeter of water at a certain temperature, the gram has not been defined in this manner for over a century (since 1889).

Many units used today are now defined in different terms than their historical origins, even non-metric units. For example, the inch is formally defined today (since 1958) as being exactly 2.54 centimeters.

Help me out here. I seem to remember from high-school physics that there were something like MKS units and cgs units. MKS stood for Meter Kilogram Second, while cgs stood for centimeter gram second (or something like that, I really can’t bring it to float). Thus there was a MKS unit for force (Newton?) and a cgs unit (dinas?).

I don’t think I really have a point to make here. Just remembering some obscure factoid that might be of use to the discussion.

What MKS and cgs means is that at some point someone did find grams small for something and started using bigger units.

BTW: small mass measures aren’t unique to the metric standard. The grain is only about 64 milligrams.