Weight of a gallon of water

General
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weight of a gallon of water

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What is the weight of a gallon of water?

Answer: The weight of a gallon of water is a common question, and the answer depends on the temperature of the water. Here’s a detailed explanation:

Standard Considerations:

  1. Definition of a Gallon:

    • In the United States, a gallon is defined as 231 cubic inches or 3.78541 liters.
    • In the UK, a gallon (imperial gallon) is defined as 277.42 cubic inches or approximately 4.54609 liters.

  2. General Approximation:

    • For many practical purposes, it’s common to use the estimate that a U.S. gallon of water weighs about 8.34 pounds (lbs) or approximately 3.78 kilograms (kg).

Scientific Breakdown:

  1. Density of Water:

    • The density of water is approximately (1 , \text{gram per cubic centimeter} (1 , \text{g/cm}^3)) at typical surface temperatures (around 4°C or 39°F).
    • Density varies slightly with temperature because water expands slightly as it warms up and contracts as it cools down.

  2. Weight Calculation:

    • Volume of U.S. gallon in cubic centimeters:
      1 \, \text{gallon} = 3.78541 \, \text{liters} = 3,785.41 \, \text{cm}^3
    • Since the density of water is (1 , \text{g/cm}^3), the weight in grams is equal to the volume in cubic centimeters:
      \text{Weight} = 3,785.41 \, \text{grams}

  3. Conversion to Pounds:

    • There are approximately 453.59237 grams in a pound.
    • Converting grams to pounds:
      \text{Weight in pounds} = \frac{3,785.41}{453.59237} \approx 8.34 \, \text{pounds}

Temperature Effects:

  • At 4°C (39°F):
    • Water is at its densest state, and one gallon will weigh the most, about 8.345 pounds.
  • At room temperature (~20°C or 68°F):
    • The weight of one gallon of water is slightly less due to decreased density, but it remains very close to the standard 8.34 pounds.

Final Answer:
A U.S. gallon of water weighs approximately 8.34 pounds (lbs) or 3.78 kilograms (kg) under standard conditions. Variations in temperature can cause slight differences in this weight.

For scientific accuracy and practical use, you can refer to this weight for most everyday calculations and considerations involving a gallon of water.