The weight of rock is definite and does not change. If the rock weighs 10 pounds, it will always weigh 10 pounds. However, the weight of water is not a definite measurement. The weight of a gallon of water fluctuates with the temperature and the density of the liquid.
Why does the temperature and density of water affect the weight of the water? You have to consider that a gallon is a unit of measurement. A specific amount of water is required to make a gallon of water. When the temperature surrounding the water increases, the energy of the water increases. When the temperature surrounding the water decreases, then the energy of the water decreases.
The weight fluctuation is caused by the number of molecules in the water. As the temperature surrounding the water rises, the number of molecules in the water increases. When the molecules of water increase the density of the water is lowered. You could say that the water gets thinner as the temperature rises.
The actual weight of the water does not change because of the temperature the only things that change the weight of the water are the density of the water or the mass of the water. The reason this changes the weight of a gallon of water is that a different amount of water will be needed to fill a container when the density and mass of the water are altered.
Another consideration is the weight of water is the atmospheric pressure and the amount of gravity the water is being subjected to. On earth, the atmospheric pressure and gravitational pull are greater than they are on the moon. So a gallon of water on earth weighs more than a gallon of water on the moon weighs.
It behooves us to know how much water weighs so we can determine how much water we can carry, or how much water we can place in a container before we exceed the weight limits of the container.
To determine the weight of the water a container will be able to handle you should measure the container. The size of the container will dictate the amount of gallons of water that can be placed inside it. Once you know how many gallons of water a container will hold you can multiply the number of gallons by 8.3 and you will have the approximate weight of the water in the container.
You should remember to consider the weight of the empty container when you are making these calculations. The thickness of the material that your container is made of, and the type of material the container is made of, will alter the weight of the container.
The following chart will help you discern the weight of water that your container will hold.
Measure | Ounces | Pounds | Grams | Kilograms |
| teaspoon | 0.1739 ounces | 0.0109 pounds | 4.929 grams | 0.004959 kilograms |
| tablespoon | 0.5216 ounces | 0.0326 pounds | 14.787 grams | 0.0148 kilograms |
| cup | 8.345 ounces | 0.5216 pounds | 236.59 grams | 0.2366 kilograms |
| Pint (2 cups) | 16.691 ounces | 1.043 pounds | 473.18 grams | 0.4732 kilograms |
| Quart (2 pints) | 33.382 ounces | 2.086 pounds | 946.35 grams | 0.9464 kilograms |
| Gallon (4 quarts) | 133.53 ounces | 8.345 pounds | 3,785.4 grams | 3,785 kilograms |
| liter | 35.274 ounces | 2.2505 pounds | 1000,000 grams | 1,000 kilograms |
How much does a gallon of water weigh frozen?
The tricky part of this question is that when water is frozen the mass of the water changes. The water molecules expand as the water freezes. When the water molecules expand the water will need to occupy a larger space.
- Technically one gallon of water does not have a weight change when it freezes; it has a density and mass change.
- Typically in the liquid form, a gallon of water weighs about 8 pounds using the standard liquid United States measurement. If you have a container that can hold one gallon of liquid water and you fill it with one gallon of frozen water, the frozen water would weigh closer to 7.5598405 pounds.
- Typically water in its liquid state has a density of 1.0. Frozen water, or ice, has a density of 0.9169.
- One half of a gallon of ice would weigh about 3.8 pounds. One half of a gallon of liquid water would weigh about 4 pounds.
- Frozen water weighs slightly less than liquid water because when the frozen water is thawed there will not be as much liquid water in your container.
How much does 5 gallons of water weigh?
For everyone who uses the liquid gallon measurement that is preferred in the United States five gallons of water weighs roughly 40 pounds.
If you are measuring your water weight using the imperial pound as a tool then five gallons of water weighs 50.1 pounds.
If you are using the dry United States pound as a guideline then 5 gallons of water would weigh 48.55 pounds.
Remember that a five gallon bucket or container will hold a larger amount of water in its liquid state. If you fill a five gallon bucket with frozen water then the bucket will hold less of the substance and the weight of the water in the bucket will be altered.
How much does a liter of water weigh?
People who use the metric system of measurement will know that one liter of water weighs one kilogram because one liter is the equivalent of one kilogram. Using these calculations we discover that one milliliter of water is determined to weigh about 1 gram.
When using the United States liquid gallon measurement one gallon of water is determined to weigh about8.3 pounds. That is the equivalent of 3.785 liters. If you divide 3.785 liters into 8.3 you will find that one liter of water weighs 2.1928 pounds.
How much does a gallon of water weigh in pounds?
To determine the weight of water in pounds, you must first determine the definition of pounds. The word pound does infer a unit of weight measurement, but this unit of weight measurement is taken in three common ways.
In Canada and in the United Kingdom the weight measurement in pounds is greater than it would be in the United States. In Canada and the United Kingdom, and in several other countries, the word pound refers to the imperial pound. The imperial pound of a liquid such as water is basically 4.546 liters. The pound equivalent of those liters is 10.02.
In the United States, and all countries that use the United States standards of measure there are actually 2 different pound measurements. The United States uses the liquid pound measurement and the dry pound measurement. The majority of people are familiar with the liquid pound measurement used in the United States.
The liquid pound of water in the United States is the equivalent of 3.785 liters. The pound weight of those liters is equal to 8.3 pounds.
The dry pound measurement in the United States is slightly larger than the liquid. The dry pound is the equivalent of 4.405 liters. That is equal to 9.71 pounds.
The temperature and density of the liquid affect the weight of the liquid. It is commonly agreed that a gallon of water weighs about 8 pounds when it is at its density state.
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How much do 100 gallons of water weigh?
If you are measuring the gallon of water using the United States liquid gallon measurement then 100 gallons of water will weigh about 800 pounds. Of course, temperature and density might increase that number or decrease that number slightly.
If you are using the dry pound measurement used by the United States 100 gallons of water would weigh 971 pounds. This unit of measurement is rarely used, and it does not reflect the true amount of liquid that it takes to fill a container. That is why you have dry ingredient measuring cups and liquid ingredient measuring cups in your kitchen.
The dry ingredients and the liquid ingredients take up a different amount of space to create one cup. You cannot get an accurate measurement of a liquid if you are using a dry ingredient measuring system.
If you are using the imperial pound measurement used in Canada and the United Kingdom then 100 gallons of water would weigh 1,002 pounds.
Final note
Water is like all liquids in the fact that the density of the water changes the actual weight of the water. The denser water is thicker and the molecules are closer together. The cold temperature of the air surrounding the liquid causes the density of the liquid to change.
For the most part, people accept that water weighs about 8.3 pounds. Many people round that number down to 8 pounds. 8 pounds per gallon is sufficient to figure out how much weight you are carrying when you bring home a gallon of water, or how much weight a platform will need to be able to support if you are going to place a specific number of gallons of water on that platform.
You’ll have to clarify your findings. I’ve been a biochemist for 30 years and any scientist knows if you fill a gallon container with water and record the weight, then heat the water, molecules don’t suddenly appear making the container weigh more. It will always weigh what it weighs. Only density changes which changes volume, not weight. By stating you have more molecules when heated you just violated the Law of Conservation of Mass*. To a student new to chemistry it’s misleading. I cringe while reading it, and a simple rewording could clarify the issue.
*(In physics and chemistry, the law of conservation of mass or principle of mass conservation states that for any system closed to all transfers of matter, the mass of the system must remain constant over time, as the system’s mass cannot change, so quantity can neither be added nor be removed. Therefore, the quantity of mass is conserved over time.). Mass within a gravitation field is weight. Therefore the weight (ie mass) of a closed system cannot change.
PS. Water is a poor example for density vs temperature. If I have 0.9984g of water at 0℃, I have 1ml of volume. If I have 0.9984g of water at 8℃, I have 1ml of volume (at 1 atm). As water cools it crosses a density gradient where it’s becoming more dense then less dense.