Randy Hi, I dont quite understand what you want when you say you want to measure the lenght of your stringers,? And am I to understand your stairs are a straight run, or do they turn at the top or bottom.
If its a straight run, no problem "where have I heard that before", Measure the hight from the basement floor to the floor above."lets call that the rise." Now the lenght. "lets call that the "run" but we will talk about that later. Divide the rise (floor to floor) into equal parts, (about right will not do) measure within 1/16" not more or less. The line that you have drawn will be the top of the tread. Lenght lines are next, divide the lenght again into equal parts but allow 2" over lap of the tread (at the leading edge ) the front part. If you allow between 6" to 8" rise between each tread, you should get your lenght of string.. Myself: I draw it all on the wall, if you cant,then draw it on two sheets of hardboard/plywood, 8'x 4' should do. The drawing you do on the sheets will be real size, and you can see if you have a problem (before you start cutting the timbers)
If you have bend in your stairs the it's the same but with a lot more detail. Have fun. John 2000