Different sources suggest varying results but a 5 gallon bucket of dry sand weighs in the 60-70 pounds range.
According to Aqua-calc.com, sand (dry) weighs 1.602 gram per (cubic centimeter) or 0.926 ounce per cubic inch, meaning a full 5 gallon bucket weighs about 67 pounds (30,321 g or 1,070 oz).
On the other hand, TraditionalOven.com says that 1 gallon of beach sand is equivalent to 12.76 pounds (lb) in weight, meaning a full 5 gallon bucket weighs about 64 pounds.
The problem with converting volume to weight is that it isn't as simple as it sounds.
Before you can go any further with your calculation, you need to find out the density of the substance that you are trying to convert. You should be aware that densities vary based upon temperature, where liquids are concerned.
See densities of some common materials from EngineeringToolbox.com.
Learn more on how to work out this kind of conversion on TheCalculatorSite.com.