Linear speed calculation

i have a rotary encoder that sets on a roll and material travels over the roll. i need to calculate linear speed as my material travels over my roll.
I have a micro 1400 and a 500ppr encoder, my estimated speed is about 1-2ft/min
is all i need ft/min=rpm x circ ????

thanks

You would need to know the circumference of the pitch diameter that is driving the encoder. If your encoder gives a RPM output then calculating the FPM would be simple math.

If you will have to count how many pulses there are in a time period then you will have to calculate how many pulses in a certain time period to get the FPM