If out of the blue, someone asked you how much water weighs, you may be confused. Water is a liquid, and liquids are typically measured in volume, not weight.
But on second thought, you remember that water is matter, and everything that is matter has weight.
So, how much does water weigh? The weight of water is not quite as fixed as the weight of solid substances. Water’s weight fluctuates with temperature changes. It also changes depending on the presence or absence of dissolved substances.
As we already hinted, the weight of water is not fixed. This means that under different conditions, water may weigh less or weigh more. In this article, we will be exploring the variation of the weight of water.
How Much Does Water Weigh?
There is no constant weight for water.
As the temperature changes, the weight of water changes.
Also, without dissolved substances, water weighs less. But with dissolved substances like salt and sugar, water weighs more.
Notwithstanding the information above, there is a generally accepted value for the weight of water. At room temperature (70 °F), 1 gallon of water weighs an average of 8.33 pounds.
Normally, most liquids progressively get heavier as the temperature falls. But, there is a unique phenomenon with water.
As water becomes colder, it does indeed become heavier. But at 39.2 °F, water is at its heaviest—weighing 8.45 pounds per gallon. Then as water goes colder below this temperature, it becomes slightly lighter again.
You could try this out yourself at home. Weigh a cup of water at 180 °F and another cup of water at 50 °F. The difference between the weights of these two samples should be about 0.2-0.25 pounds.
You could also try weighing a cup of water containing 1 tablespoon of sugar against a plain cup of water. The sweetened water should weigh more than the plain water.
Different Types of Water Measurements
As you may already know, water can be measured in various units. It can be measured in gallons, cubic feet, acre-feet, amongst others. In this section, we will discuss some of the units of water measurements and their weight equivalents.
A gallon of water equals approximately 16 cups of water and weighs 8.33 pounds at room temperature. The same quantity weighs 8.45 pounds at 39.2 °F and 8 pounds at the boiling point (212 °F).
A cubic foot of water equals 7.5 gallons of water (approximately 118 cups of water). At room temperature, 1 cubic foot of water weighs about 62.48 pounds.
At 39.2 °F, this same volume of water weighs 63.38 pounds, and at the boiling point, it weighs 60 pounds.
An ounce of water equals 0.00781 gallons of water. This, in turn, is about 0.12 cup of water. At room temperature, 1 ounce of water would weigh 0.065 pounds. While at the boiling point, it would weigh 0.063 pounds.
The maximum weight of 1 ounce of water (weight at 39.2 °F) is around 0.066 pounds.
At room temperature, 1 pound of water equals 0.12 gallons (approximately 2 cups of water). At the boiling point, 1 pound of water equals 0.125 gallons. While at 39.2 °F, 1 pound of water equals 0.1198 gallons.
A liter of water equals 0.264 gallons of water (approximately 4.2 cups of water). A liter of water weighs 2.2 pounds at room temperature.
At the boiling point, 1 liter of water would weigh around 2.112 pounds. Then at 39.2 °F, 1 liter of water would weigh 2.203 pounds.
An acre-foot is the unit of measurement for water that is impounded or stored. An acre-foot of water equals 325,851 gallons of water. At room temperature, one acre-foot of water would weigh about 2,713,974.056 pounds.
When cooled to around 39.2 °F, an acre-foot of water would weigh 2,719,358.386 pounds. But when boiled to 212 °F, it would weigh 2,606,912.917 pounds.
Weight of Freshwater vs. Seawater
Remember earlier we said the presence or absence of dissolved substances in water would affect its weight? Well, that applies here.
Seawater is heavier than freshwater or pure water, and this is due to the presence of dissolved salts in seawater. While 1 gallon of fresh water weighs around 8.3 pounds, the same volume of seawater weighs 8.6 pounds.
In the table below, we compare the weight of various measurements of pure water and seawater.
Table Showing the Weight of Salt Water vs. Sea Water at Room Temperature
|Measurement||Pure Water (lbs.)||Salt Water (lbs.)|
At room temperature (70°F), 1 cup of water weighs around 0.53 pounds. The weight of a given volume of water will always vary depending on temperature.
So it is better to always reference the temperature of the water when it was weighed. Besides temperature, salt, sugar, and similar water-soluble substances also affect the weight of water.