Unwrap the curve = you have length = L
then draw a circle : L= 2 *pi * R so Radius = L / (2*pi)
you can enter directly formula inside the box dialog of the circle for Radius! :) enter pi as the two letters pi !

unwrap: http://moi3d.com/forum/messages.php?webtag=MOI&msg=5136.1

Ps Click on the Size box number for have the exact length for make your copy / past of the numeric L !!!
Because that you show on the up corner screen is troncated or approach value!