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I have the following equation:


to: convert kg to lbs, divide by $2$, then convert the result from oz to L

is there a shortcut to do this without the conversion to imperial?

yeah, I know this is probably a very elementary question, math has never been my strong suit.

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The kilogram is a unit of mass, while the liter is a unit of volume... – J. M. Aug 9 '12 at 13:40
What are you actually trying to calculate? – celtschk Aug 9 '12 at 13:48
this is a nutrition thing: basic amount of water before factoring in environment, etc = half of body weight (in pounds) in oz of water per day, hence the mass to volume conversion. – bee.catt Aug 9 '12 at 13:53
"this is a nutrition thing: basic amount of water before factoring in environment" - should've mentioned that to begin with. Where did you obtain this formula? – J. M. Aug 9 '12 at 13:56
sorry, J.M., I should have explained that better. If you mean the equation for lbs:oz, I have found it in various places, couldn't give you an exact reference without searching it out again, it gives a similar result to 1L:1000cal. As for the equation above, it was what I was able to come up with myself to take a stored metric value, perform the imperial equation, and return a metric result. – bee.catt Aug 9 '12 at 14:04
up vote 1 down vote accepted

$1$ pound is $16$ ounces, and $1$ litre of water has mass very, very close to a kilogram (apparently only about 0.999975 kg). So you should be able to multiply the mass in kg by $\frac{1}{32} = \frac{1}{2} * \frac{1}{16}$ to get effectively the same result.

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Thank you very much, this seems to give a satisfactory result. In my case, I expressed it as kg*0.03125, is this correct? – bee.catt Aug 9 '12 at 14:32
@bee.catt It's the same – Cocopuffs Aug 9 '12 at 15:22
That is, half an ounce per pound. But OP's formula (and yours as well) do not account for the mass of a liter (which has nothing to do with the problem); they both also ignore the difference between a pound of water (weight) and 16 fluid ounces of water (a US fluid pint, by volume, which weighs 1.04375 pounds, despite the American saying "A pint's a pound".) However, if it clear that the assumption_is that the body weight is in _pounds avoirdupois, but the water is measured in US fluid ounces, the difference between a pint and a pound doesn't matter. – Brian Hitchcock Jul 29 '15 at 9:29
But keep in mind, if you are in a Commonwealth country that uses Imperial fluid ounces, you don't need quite as many as you would of US fluid ounces, because an Imperial fluid ounce is about 4% bigger than a US fluid ounce. – Brian Hitchcock Jul 29 '15 at 9:40

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