Specific gravity is the density of an object compared to the density of water. Therefore, knowing the specific gravity of the substance is important for converting pounds to liters. A specific gravity greater than 1 is more dense than water (lead weights), while a specific gravity less than 1 is less dense than water (cotton swabs). The density of water is 2.19 pounds per liter.

Divide the weight of the item you wish to convert by the specific gravity of the object. This converts the weight of the object to what the weight would be if the object was water.

For example, a 657 pound item with specific gravity of 1.5 would equal 438 pounds if it were water.

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Divide the resulting weight by 2.19 - the weight in pounds of 1 liter of water.

In the example, 438 pounds would become 200 liters.

The result is equal to the amount in liters of the weight of your object.

Completing the example, the 657 pound item with a specific gravity of 1.5 converts to 200 liters.