Find the density of antifreeze. According to the Techguys site, the density of common antifreeze made of ethylene glycol is 1.114 grams per milliliter, but different antifreeze may have a different density.
Visit a Web-based conversion site to perform density conversions. The following instructions are for Online Conversion (see Resources).
Scroll down to gram/milliliter on the left and pound/gallon on the right.
Enter 1.114 (or the density of your antifreeze) in the box next to "Convert what quantity?"
Click "Convert" and read your answer. Here, it rounds to 9.3 pounds per gallon, so one gallon of this type of antifreeze weighs 9.3 pounds.
Convert from pounds of antifreeze to gallons by dividing the weight by the pounds-per-gallon figure, in this case 9.3. Thus, 20 pounds of this type of antifreeze would measure 2.15 gallons.Gallons are measures of volume and pounds are measure of weight, therefore, it is not possible to convert from one to the other without additional information. To figure out how much a gallon of antifreeze weighs, you'll need to know its density.