There are about 7.5 gallons per cubic foot, so 16 gallons is a little over two cubic feet. A typical bag of premixed concrete makes one cubic foot of concrete, although there are different sizes so you need to check how much the specific bag you intend to purchase will make. If it is one bag per cubic foot, you will need a little over two bags to fill the bin. Concrete weighs about 150 pounds per cubic foot, so you bin will be a little over 300 pounds when full.
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