8.35 pounds US.

Weight of 1 US Gallon of water = approx. 8.34 lb. If you take time to read the question you will find out the person is asking for the weight of one/a gallon of water... not ice, so the answer is 8.345404487293294 pounds or ~8.35 pounds is applicable in most scenarios. Short answer: 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. From a cook's perspective: There is an old cooking phrase that addresses the weight of water and other similar liquids (and in some cases, solids) used in the preparation of foods: "A pint's a pound the whole world 'round." Actually, a US pint of water weighs 1.04375 pounds, or an imperial pint of 20 ounces weighs 20/16=1.25 pounds. So this phrase is rather inaccurate in both systems! There are eight pints in any sort of gallon. Using this rule, a gallon (eight pints) would weigh approximately eight pounds, while a more accurate figure is 8.35 pounds (or 10 pounds) per gallon. Although pints of milk, gravies, and sauces are denser and actually weigh more than a pint of water, the cook can generally use his/her own judgment as to how much other liquids actually weigh. If you have an accurate weight scale, you can quite easily verify these figures. From a meteorologist's perspective: You must first define the system of weight you will use. Traditionally, this is the avoirdupois weight system for coarse measurement used in the English System of weights and measures. That system defines one pound as being equal to 16 ounces. The US gallon is defined as 231 cubic inches, which was an old "wine gallon" measure. A pint is therefore 28.875 cubic inches which does not, unfortunately, weigh 16 ounces. Nevertheless, a volume unit used in the US is the "fluid ounce," one-sixteenth of a US pint, or 1.8047 cubic inches. The imperial (UK) gallon is defined as 10 pounds of pure water at 62 degrees Fahrenheit at a barometric pressure of 30 inches of mercury. The measure must be taken on scales, with the water suspended in the air and measured with brass weights. In the imperial system, with 8 pints in a gallon, a pint is 20 fluid ounces, so a fluid ounce of water does weigh one ounce (exactly, under the prescribed conditions). Here are more answers from other WikiAnswers contributors (but the figures aren't all consistent): Using the US system, a gallon (231 cubic inches) of water at its maximum density, chilled to 3.98 degrees centigrade, weighs 8.3389 avoirdupois pounds. One liter of water has a mass of 1 kg., and 1 gallon of water is equal to 3.7854118 liters; therefore, 1 gallon has a mass of 3.7854118 kg, which is 8.345404487293294 pounds. The weight of 1 Kg is approximately 10N. But at what temperature? Temperature matters. 1 gallon of fresh water is about 8.36 pounds. According to the 21st edition of The Machinery's Handbook, 1 gallon of water weighs 8.337 pounds. To answer this question more appropriately, you would have to know the temperature of the water. As water cools it becomes denser until it reaches 39.2 degrees Fahrenheit. Below this temperature, the density decreases and the water molecules spread apart. One liter of water/ice at this temperature will actually weigh less than one liter of water at, say, 80 degrees Fahrenheit. The Handbook of Chemistry and Physics specifies the weight of 1 US gallon of water in air at 68 degrees F to be 8.32487 pounds or 3776.103 grams. To say the temperature of the water affects the weight is somewhat misleading. If you take 1 gallon of room temperature water and place it in a sealed container, the weight will not change regardless of the temperature, although it will not remain exactly one gallon. Weight is the measure of the pull of gravity on the mass of an object. The mass of water will not change based on temperature, therefore the weight will not change. To be more accurate, the temperature of the water will affect its density. Ice takes up more space than liquid water. Therefore, a gallon of ice will contain less mass than a gallon of room-temperature water. However, it's useful enough to know that one gallon of water weighs about 8-1/3 lb. A gallon is not a measure of mass but a measure of volume, and water at different temperatures has different volume-to-mass ratios. A gallon of ice and a gallon of water at room temperature have different weights even though they are the same size, that is, occupy the same volume. One gallon of water, at 20 degrees Celsius, weighs 8.33 pounds. A U.S. gallon (determined by fluid volume at 72 deg. F, at sea level) of fresh water weighs exactly 8.3452641 lb. http:/acethepartyplace.com/master.html?http:/acethepartyplace.com/info-p/pp_stan.html Equivalent Conversions 1 ft**3 of water = 7.48 gallons 1 ft**3 of water weight = 62.38 lb. 1 in**3 of water = .00433 gallons 1 in**3 of water weight = .0361 lb. 1 gallon of water = 231 in.3 1 gallon of water weight = 8.34 lb. It looks like one gallon of water weighs 8.34 Lbs. If you consider small changes with temperature, then what about location? If you took a gallon of water up a mountain or into space, it would be minutely farther from the center of the Earth and weigh minutely less. If it were taken into deep space, it would weigh next to nothing (although its mass would stay the same). On Jupiter, it would weigh about 19.5 pounds.