I've been using the GNU units program and I seem to think that I should be able to convert water between a volume and a weight.


You have: 1 gram water
You want: cm^3
conformability error
    1 gram water = 9.80665 kg^2 / m^2 s^2
    cm^3 = 1e-06 m^3


You have: 1 gallon water
You want: pounds
conformability error
    1 gallon water = 37.122208 kg m / s^2
    pounds = 0.45359237 kg

The water unit is the specific weight of water at the standard temperature of 0°C. A cm water is a unit of pressure, like the cm Hg.

You have: water
You want: 
        Definition: gram force/cm^3 = 9806.65 kg / m^2 s^2

You have: 1cm Hg
You want: cm water
        * 13.5951
        / 0.073555914

A gram water is a unit of mass times pressume divided by length, which I don't recognize as a common physical quantity. Units has waterdensity defined to be the density of water at 4°C and 1atm, which is (to a very good precision) 1kg/m³.

You have: 1g/waterdensity
You want: cm^3
        * 1
        / 1

If you want density in other conditions or of other materials, either type out the constant or put it in your own unit definition file (units -f '' -f ~/.units.data).


Technically speaking, you're trying to convert volume into mass or weight. Sure, you wrote "water", but at what temperature and pressure? It makes a difference. And what if you wrote "1 gram mercury"?

You're asking for something that can't be done in the simplistic context in which units works. I think you're going to have to look up the density of the fluid you're interested in, and multiply by yourself.

  • -1, GNU units does actually have a limited selection of densities in its database, it's just that the keyword is waterdensity, not water. – Random832 Jun 28 '11 at 17:20

Your Answer

By clicking “Post Your Answer”, you agree to our terms of service, privacy policy and cookie policy

Not the answer you're looking for? Browse other questions tagged or ask your own question.