1 gallon = 3.78 liters
First of all, because Kg is a measurement of mass and a liter is a volume there cannot be a direct conversion factor because various materials have different densities. You need to know the Specific Density of the material. SG is a ratio (usually expressed as a decimal) that compares the density of a material with water. Water is given SG 1.00 so a piece of lead will have SG greater than 1.00 and most of SG wood is less than 1.00 One constant is liquid water where 1Kg = 1Ltr so if that is your problem, then it is conversion 1: 1 straight
Because this is 1 Liter equal to 1 kg
if 5 gallone = 18.92 ltr = 18.92 kg
It is also important that 1 Gallon is around 3.78 liters and
then 5 Gallons will be around 18.9 liters.
1 liter of water has a mass almost exactly 1 KG when measured at its maximum density, which occurs at around 4 ° C
For that we can also say that 5 Gallons = 18.9 liters = 18.9 KG = 41.7 Lbs
Almost all the other answers here are correct (with varying degrees of precision) but basically say that the weight of water (for US gallons) is 8.34 pounds so much with 5 and your answer is lbs.
But because you may have studied in class, or at least heard somewhere, cold water is denser than warm water, which is why water comes to the south from the arctic region (in general, mainly because of melting ice) sinks under running water heaters to the north, arriving from Florida in the current of the Gulf Stream. This effect is important for maintaining large ocean currents flowing, but also shows that 8.34 or 8,345 or even 8.345404 pounds are standard quantities at certain standard temperatures and pressures.
Water on the ocean floor, or a very, very deep lake (because saltwater does not have the same density as fresh water) is compressed by all the large loads of water above it, so that a gallon of water weighing 40,000 pounds per square inch will feel heavier than 5 gallons at standard pressure and temperature.
Also because you might know, when the water freezes expands (that’s why it floats ice). Because it is less dense than liquid water, the 5 gallons occupies 231 cubic inches by 5 times, but the ice weighs only 91.85370741442966. Therefore the standard weight of 5 gallons of US frozen water 5 X 0.9185370741382966 X 8.345404 which is around 38.32781486342745 pounds. Ice, however, gets denser because it gets colder so the difference in weight is less at much cooler temperatures.
Then there is the case of 5 gallons of water that has been heated to 101 degrees Celsius, which means that it will turn into steam, which, again, varies in density according to temperature and pressure. So considering all these strange and unusual cases, you can see that it is helpful to have more information about your 5 gallons of specific water, such as where, at what temperature, what salt can be dissolved in it (all water is from the mountain stream or from your faucet in the kitchen sink has some minerals that dissolve in it, except carefully distilled water where the distillation process leaves these minerals), or whether the distilled water is pure.
You may have to take one of the other answers. Because you ask questions like you do, chances are you won’t find this strange and unique situation valuable, except knowing that what we learn in school is almost always “wrong”
Education is needed. Most of what is taught is wrong. It may also be fun, and fun for students and for teachers (who usually teach the same thing year after year to students of the same age and class).
I hope it is help, not in getting answers but in understanding that there is no single “right” answer.