Modeling a low pass filter?

I have come up with the coefficients in a software lowpass filter that I have used to model a circuit to behave how I want. I am having trouble finding a site that will let me enter the values into a formula and calculate what R/C (Resistor/Capacitor) values I need to recreate that software filter as a hardware circuit. Can anyone point me to something like that?

Give this link a try: RC Low-pass Filter Design Tool