I'll give you some common coins and their mint weights and silver composition. You can calculate from there!
Jefferson Nickel: 1942-1945, 1942 had some nickel and some silver five cent pieces, They are distinguished by the large mint mark over Monticello for the silver, 1942-1945 .05626 oz. silver. 56% silver content.
Winged Liberty Head, Mercury, Dime: Coin weight 2.50 grams, 90% silver, 0.07234 oz. pure silver.
Roosevelt Dime: 2.50 grams total weight, 90% silver, .07234 oz. pure silver.
Washington Quarter: 6.25 grams, 90% silver, .18084 oz. pure silver.
Franklin Halk: 12.50 grams, 90% silver, .36169 oz. pure silver.
Kennedy Half: Year 1964, 12.50 grams, 90% silver, .3169 oz. pure silver.
Years 1956-1969 &1970 D&S, 11.50 grams, known as 40%, I don't have the actual silver content to calculate from.
Liberty Head or Morgan Dollar: 28.73 grams, 90% silver, .77344 oz. pure silver.
Peace Dollar: 26.73 grams, 90% silver, .77344 oz. pure silver.
All this info is in the Whitman Red Book.
Midwest Refineries in Michigan pays the highest rate, 94% of the current price for silver, gold and platinum. I would take it that they weigh the items sent in and would determine the amount paid from there. I sent in some items recently and was very happy with the outcome. Hope this helps.
HH