How Much Does A 55 Gallon Fish Tank Weigh? (Check This First) A 55-gallon tank weighs about 42 pounds when made of acrylic and about 78 pounds when made of glass, but requires 2.5 gallons of water for every gallon of gas. How much does a full 55-gallon barrel weigh? Fifty-five gallons of water equates to 459 pounds, so you're looking at around 500 pounds if you use the drum. Depending on the density of ...