How Much Does Water Weigh? Calculators, Charts & Guide (2024)

ByJack Gray, Roof Online Editor• Last updated July 27, 2024

Table of Contents

• Water Weight Calculator (by Area and Depth)
• How to Calculate the Weight of Water
• Weight of Water by Unit of Volume
  • About This Table
  • Table 1: Weight of Water by Unit of Volume
• Weight of Water by Temperature
  • Table 2: Density of Water by Temperature
• Water Weight per Inch per Square Foot
  • About This Table
  • Table 3: Weight of Water per Inch per Square Foot
• Related Articles

Water Weight Calculator (by Unit & Temp.)

Note that water is at maximum density (or weight per unit of volume) at 39.2°F/4.0°C. The weight of water is usually given for water at maximum density by default, but we are using room temperature (70°F) as the default setting.

If you select a temperature other than 39.2°F/4.0°C, the weight values calculated will likely be slightly different than water weight values found elsewhere.

Water Weight Calculator (by Area and Depth)

How to Calculate the Weight of Water

To find the weight of water, you need to pick which unit of volume you want to use to measure the water, and then figure out how many of these units your quantity of water contains. All of the most common units of volume are included in Table 1 below.

Once you know the type of unit and the number of units, refer to the weight of your unit given in Table 1, and multiply the weight for one of those units by the number of units you have.

Next you need to adjust the weight to account for the temperature of the water.

The weights given in Table 1 are for water at maximum density, which water achieves at 39.2°F (or 4°C). The density of water changes with the temperature of the water, so the mass of a particular volume of water changes with the temperature as well, which means that the weight also changes.

Table 2 below shows water density by temperature, and the second column in the table shows the percentage of maximum density for each temperature. You can select your temperature and see what percentage of maximum density it is.

Since the weight value you got from table 1 is for maximum density, you can multiply the weight from Table 1 by the percentage from Table 2 to get the actual weight of the water you are concerned with.

Example:

How much does 100 gallons of water weigh at room temperature?

Step 1:

According to Table 1, a gallon of water weighs 8.34540 pounds at maximum density.

Step 2:

8.34540 x 100 = 834.54 pounds

100 gallons of water weighs 834.54 pounds at maximum density.

Step 3:

According to Table 2, the density of water at room temperature (70°F) is 99.802% of the density of water at 39.2°F (maximum density).

Multiply 834.54 pounds by 0.99802 to get 832.8876108 pounds, which we would round off to 832.89 pounds.

So 100 gallons of water weighs 832.89 pounds at room temperature.

Weight of Water by Unit of Volume

About This Table

The following table gives the weight of water per unit for all of the common measurement units used to measure liquid volume. The weight values provided are for pure water at maximum density, which occurs at 39.2° Fahrenheit or 4.0° Celsius.

Weight of water and temperature: Note that the density of water at room temperature will be 0.00198 g/cm³ less than water at its maximum density (see the next table below). We are assuming room temperature to be 70°F (21°C) for simplicity’s sake.

You can figure that the weight of water at room temperature for any specific volume will be approximately 99.8 percent of the weight of the same volume of water at 39.2°F (4.0°C). For example, a cubic foot of water at room temperature will weigh 62.3044 lbs., which is approximately 99.8% of the 62.4280 lbs. that a cubic foot of water weighs at 39.2°F (4.0°C)

We are aware that a mole of water is a specific number of water molecules and not a unit of volume but we thought we’d include it anyway.

We are also aware that a surprising number of people don’t realize that a fluid ounce is a unit of volume and not weight…

Table 1: Weight of Water by Unit of Volume

Weight of Water by Temperature

Table 2: Density of Water by Temperature

About This Table

The table below provides the weight of water per inch in pounds for various areas/square footages.

This should allow you to quickly and accurately estimate the weight of any amount of standing water on your low slope roof.

One cubic inch of water weighs 0.036127 of a pound. One square foot of water one inch deep weighs 144 times this, or 5.202288 pounds. Everything else has been calculated from this.

This table should give you an idea of how much weight a rain load could be imposing on your roof due to areas of ponding water or clogged drains.

Also see our Roof Drainage page.

Weight of water values for areas or depths not covered in the table should be easy to arrive at simply by adding together values for areas or depths which are listed.

Table 3: Weight of Water per Inch per Square Foot

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