How much $1 billion weighs depends on how much money was used to make it. If money only came in $100 bills, a billion dollars would weigh about 10 tonnes. Using $1 bills, a billion dollars would weigh 1,000 tonnes, or 2 million pounds.
Also, $1 million worth of $100 bills weighs about 22 pounds. In the same way, a million dollars worth of $1 bills would weigh a little more than a tonne. If a person had 10 billion $1 bills and spent one every second, every day, they would have money for 319 years.