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- 1). Look on the propane tank's label for the tare weight, which is labeled as "TW." It might also say "Weight (empty)." This is the weight of an empty tank. As an example, a 7.1 gallon tank might have an emplty weight of 24 pounds.
- 2). Place the propane tank on a weigh scale and record it's weight. As an example, if it read 40 pounds, you know there is at least some propane left in the tank, since it weighs more than the tank would when empty.
- 3). Subtract the weight you measured by the weight when empty. This will give you the weight of the propane in the tank. In the example, 40 pounds minus 24 pounds, leaves16 pounds attributable to propane.
- 4). Divide the weight of the propane by the 4.23 pounds per gallon, which is the weight of liquid propane. This calculation will give you the number of gallons left. In the example, 16 pounds divided by 4.23 pounds per gallon, tells you that 3.78 gallons of propane is left in the tank.
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