How much does one gallon of water weigh?

(8) On January 14, 2012 at 3:27 pm Jonnygouda [0] said:

OK. So far what I've read has been interesting and it is certainly true that the weight of water is different at different temperatures, air pressure and altitude/topography (there is a very small difference between the force of gravity at one place and the force of gravity elsewhere). So the REAL question (to which I have not yet found the answer) is:

What is the weight of 1 US Gallon of water at 1 bar of pressure and a temperature (of the water and surrounding air) of 20°C (approx. 68°F)?

(7) On August 4, 2010 at 5:32 pm Steve2442 [0] said:

i just realized my mistake. I apologize was wrong with my previous statement. The volume of a particular mass of a substance can change with heat and pressure there for changing the amount(mass) that can fit into a gallon of space. therefor the weight of a gallon can change with pressure and heat.

Regards,

Steve

(6) On August 4, 2010 at 1:48 pm Steve2442 [0] said:

One small point to this excellent discussion you guys have going here. Many of the post here depict temperature as a variable in this problem.

for now lets talk in terms of mass: Mass is a measurement in terms of molecular amount of a substance. now keeping this in mind the mass of a gallon (being technically speaking a finite number of molecules) will not change with temperature change. although the volume might change the mass will not.

this can be tested by taking the mass of a particular amount of water in a sealed container heating it up in till it evaporates in the container and then measuring the mass again. it will not change.

now to bring this discussion back to consider weight. weight is a measurement of the force of gravity on a finite molecular amount. the only difference here is gravity. volume does not have any effect on the gravitational pull between objects. gravity is directly relative to the mass of an object. there for the only variable with changing temperature is volume. This means that the WEIGHT of 1 gallon of water will not change with a temperature change.

Now if you get real technical what could change and i emphasize the WEIGHT of a gallon of water (because, this will not effect the mass) is elevation. the farther away from an object center of mass you get the less the gravitational attraction between the objects is. The reason i say technical this is probably something that would go unnoticed in most forms of measuring. and would be a fluctuation in the 4th or 5th decimal point when considering most places on earth. again we are talking about a fluctuation based on the strength of the earths gravitational pull and not the atmospheric pressure. so this would be disassociated with the 1 ATM mentioned above.

if anyone reads this haha pardon my momentary nerdyness i usually refrain but i felt a correct conceptual understanding of the basic principles is important and commonly confused.

Regards,

Steve

(5) On April 23, 2010 at 3:10 pm GregorS [293] said:

One US gal is 3.785+ liters but on UK gal is 4.546+ liters.

(4) On March 2, 2010 at 9:00 pm Kennmc [2] said:

A gallon is 3.78 liters. How could a gallon weigh as much as it does?

(3) On July 13, 2009 at 2:44 pm Dfoofnik [2550] said:

UK codicil: A US gallon of fresh water at 4 degrees C weighs 8.34 pounds. An imperial gallon at 62 deg F (old UK system) weighs 10 pounds.

Because a gallon is a volume, and the volume of a liquid changes with temperature, various suggestions were made which ranged from 8.3 to 8.5 lbs, but the basic answer for most applications is sufficient.

(2) On July 13, 2009 at 2:40 pm Dfoofnik [2550] said:

1611kjb said :

As can be seen from the many replies to the question, without sufficient definition there is no guaranteed correct answer. Each term must be sufficiently defined before an authoritative answer can be provided. If we define water as pure H2O, that is, water with no dissolved minerals in it that would change it's properties or the effects of other environmental variables. Next we must define a gallon. That same word is used in more than one system of measure (e.g., avoirdupois, Imperial, US, etc.). We can now sufficiently define "what" we are measuring. For this question we will clarify and state we are measuring one US gallon of pure H2O. Now we must fix the environment in which we measure it. Both the measurement of volume (1 US gallon) and weight (US pounds) are defined in terms of the temperature and pressure at which they are measured. Since we are using the United States to determine the weight and volume, we will stick with US definitions. So we must specify the standard pressure as being equal to 1 standard atmosphere, or in the US, 29.92 inches of mercury at mean sea level (MSL). Then we must set the standard temperature for the measure. Again, in the United States, that is set at 20° Centigrade. These conditions are defined by the National Institute of Standards and Technology (NIST) and are called Standards for Temperature and Pressure or STP. If you wanted to define this outside the US, you would have to use the standards for that location. For example, if you were to measure one imperial gallon in Canada, you would use the IUPAC (International Union of Pure and Applied Chemistry) standards for STP which would be 0°C at an absolute pressure of 100 kPa. Thus having defined the system of weights and measures, the thing to be evaluated and the conditions under which it is evaluated, we can say that the actual weight of 1 US gallon of pure water is 8.345404487293294 pounds. Change anything about the conditions and you will get a different answer. One gallon of tap water sitting on a picnic table in Columbus, Ohio on a sunny afternoon in July will weigh something completely different. All of the answers after this one are pointing to the kind of confusion that exists without standards (to include mathematical rules for how to round fractions).

(1) On September 19, 2008 at 5:58 am Royzourboy [0] said:

the saying states that "a pint's a pound the whole world 'round." now this is more or less a riddle. first and foremost if you are only in need of a pint or pound then this is a fine measurement. back to what this saying is actually, well, saying. the word 'round, while implying that the pint and pound are practically interchangeable most anywhere it also means to round as in mathematics. so even though a pint weighs over a pound it really is not enough of a difference to effect very much until you get up to gallon measurements and conversions.

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