That's and EXTREMELY broad question, because cents have been struck almost every year since 1793 and at three different mints.
You need to know the coins' dates, conditions, and mint marks for starters. You can then look up values at sites such as the ones linked below.
The related link below has values of all US coins and it's FREE.
The best thing to do is get a copy of "Red Book" a Guide of US coins, it has values for all US one cent coins.
If the pennies were pre-1982 then 9 US pennies are very close to 1 ounce (9.145 pennies = 1 ounce). If the pennies are after 1982 then 11 US pennies are very close to one ounce (11.34 pennies = 1 ounce).
The US never made silver pennies. In 1943 the US made steel pennies. These are often mistaken for silver pennies.
Two pennIes
For US money-21500 pennies would equal $215. There are 100 pennies to a dollar.
The diameter of a US penny is 0.75inches. There are 256 pennies in a square foot
$750.00 = 75,000 pennies (cents in the US).
There are fifty coins in a roll of US one cent coins, casually called pennies.
35,000 pennies is equivalent to 350 US Dollars. ($1=100 pennies)
1 cent the values of pennies haven't changed much
Pennies are minted at three locations in the US; The San Francisco Mint, The Denver Mint and the Philadelphia Mint. Pennies from San Francisco have an "S" on them. Pennies from Denver have a "D" on them and pennies from Philadelphia have no letter.