The face value of pre-1965 quarters and dimes is based on silver having a price of approximately $1.40 a troy ounce. You can calculate this from the fact that a pre-1965 quarter is about 1/5 troy ounce, and is about 90% silver.
This means that $1.25 is 0.9 troy ounces of silver. $1.25/.9 = $1.39.
So if you want to know the approximate spot value of your pre-1965 quarters and dimes, take the value of silver, and divide by $1.40. The coins are worth that many times their face value.
Currently, silver is $18.52/troy ounce. That comes out to about 13.23 times face vvalue.
So a pre-1965 dime is worth about $1.32, and a pre-1965 quarter is worth about $3.30.
That is all.