No other base units have a prefix, so why does mass?
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Quora said at the time of making the standards, we used a grave (which was equal to 1000 grams). It goes on that the gram was not used at the time because it was too small to measure reliably, so they went with the grave. It was switched to “kilogram” to use the standard prefix naming convention.
There are 2 variants of the system that use similar measures but, by convention, use different ones as base measure.
The SI system is MKS (meter, kilogram, second) as the base unit. The GCS system convention uses gram, centimeter and second as the base units.
The preference is somewhat mostly arbitrary and also somewhat practical. For most things we encounter and handle, MKS is the convenient measure. Scientists (especially dealing with chemistry) might prefer the GCS system. There is no “correct” measure.
MKS is consistent with many other derived units like Pascal, Newton and Joules.
When the French were developing the metric system, they suggested the unit be called a grave (pronounced grav) being the mass of 1L of water (1000 cm^(3))
The French at this time being in the middle of a revolution against the rich notice that it sounded a lot like the word Graf, being a word for Duke or Earl, and they wanted to avoid affiliating with the nobility, so they changed the measurement to be the mass of 1mL of water (1 cm^(3)) and called it the gramme
They then noticed that it was inconvenient to use a mass unit so small, so they changed back to the 1L of water definition, but kept the name gramme for the base, and threw out the word grave in favor of the kilogramme.
And that’s why the kilogram is the base SI unit and not the gram. I had the exact same question when I learned the SI unites.
Other peoples gave the initial reason (the measure used to be the grave, then the gram, then the kilogram), but you could wonder “why didn’t we changed again?”.
The kilogram is one of those many “small flaws” of the metric system, that could be corrected but would be too costly (having to recalibrate everything) for a minimal gain.
Another one of those flaw is the definition of the meter. Initially defined as 1/10,000,000 of the distance between the North pole and the equator, you might be annoyed to learn that this distance is actually equal to 10,001,965m. Similarly, many physicist are frustrated that the speed of light is 299,792,458 m/s, so almost 300,000,000 m/s, and had we defined the meter slightly differently (something like “new meter is 0.9993 old meters”) we could have had a nice round value for the speed of light.
And did you know that the temperature for boiling water is not actually 100°C, but is actually 99.975°C? Though admittedly that last one was deliberate. It was to ensure that the absolute zero was at exactly -275.15°C and not some uglier number.
Out of all of the flaws of the SI, renaming the kilogram would probably be the easiest to fix, but it’s still a lot of bother for a minimal gain.
Because that’s the unit that had the prototype mass to define it back when the definition was based on a physical object’s mass.
If you know what 1000 of something is, then you can easily find what 1 of that thing is. Kinda like how a meter is 1000 milimeters and is the standard/base unit. A single gram would be such a small measurement to use as your base it would make things more complicated.
Because for actual human measurements a kilogram is more useful. You could say the same for a Calorie with is actually a kilocalorie, but calories are so small they wouldn’t effectively convey dietary information.
Aside from the original reason, there is no real incentive to change since you wold have to either rewrite every paper or manual containing grams or check whether it was printed before or after the change which is much more laborious and costly than typing an extra k.
Alright! Think of the SI unit like a special ruler for measuring stuff. A long time ago, when scientists were picking the best size for the ruler’s main mark for weight, they thought a gram was too tiny. So, they chose the kilogram because it was a better size for lots of things they measured. Just like sometimes we use feet instead of inches for bigger distances. So, the kilogram became the main mark on our weight ruler!
It’s both: in chemistry it’s the gram because you deal with smaller things. In physics you use kg because you deal with bigger things.
To the OP: A very good and interesting question!
The answer to the OP question is: Because the “kilogram” is the base unit of mass in the coherent SI Metric System. You can’t change the base unit to the “gram” without changing all the other SI Metric units or it would then be non-coherent.
The reason is that the French waffled (see what I did there?) on their definitions of the base units and finally ended up with a thousand of the original units as their base unit.
As you can see from all the posts, this creates quite the confusion and the “kilogram” is incorrectly named and causes people to think that the “gram” is the base unit when it is not. Since it is incorrectly named, it is also incorrectly taught and people don’t learn that the kilogram is the base unit until later after they’ve already learned “gram” (because of the name).
It is incorrectly named because the SI Metric system is a very simple system with simple rules and uses a “<Number> <Prefix> <Unit>” naming scheme.
The “kilogram” is the only unit that breaks this naming scheme.
According to the SI Metric rules, you can’t say something is “500 kilokilograms”.
Therefore it ought to be renamed to something else to allow the normal usage of the mass unit with prefixes.
I propose using “klug” as new renaming for the current name “kilogram” so we can then use prefixes with the base unit of mass properly. I chose “klug” because it would have the same symbol “kg”.
I really don’t care what the name is, as long as it doesn’t have a prefix (“kilo”) in the name.
If we could rename (name change only, not redefinition) then we could deprecate the names “ton” and “gram” and only use the new name (“klug”, “grave”, something else?) as the name of the SI Metric mass base unit.
The SI Metric system is a brilliant simplification compared to all other measurement systems. The current incorrect name for the mass base unit complicates that simplicity, causes confusion and errors and creates a special case rule that has to be taken into account.
To properly use the SI Metric system, all other names for mass units should be deprecated or gotten rid of, there is no need for any other name than the base unit name when it is properly named.
1000 milliklugs (grams) = 1000 mkg = 1 klug (1 kg) = base unit of mass
1000 klugs = 1 kiloklug (same as current “metric ton”)
Yes, as is normal, it would take a long time before this new name would be used a lot but other renamings have occurred in the past. Centigrade -> Celsius, Cycles per Second -> Hertz.
I’m constantly finding web sites (even educational web sites) that claim the “gram” is the base unit of mass because of this issue. I try to contact the web administrator and get them to fix this and most sites quickly fix the issue but it is wide spread.
The SI Metric system is very good but there are several issues that I think need to be fixed with the current SI Metric System, which I’ve detailed here at the [https://github.com/metricationmatters/research](https://github.com/metricationmatters/research) URL.
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