Abstract: A device for the measurement of the diameter of a body such as a cylinder, more particularly in the form of a workpiece on a roll grinding machine, having a contact wheel adapted to run on the surface of the body and a first rotational pickup (angle encoder) centrally coupled with or provided with a the contact wheel, and a second rotational pickup, which is adapted to indicate at least full revolutions of the body. The cylinder is coupled with the second rotational pickup (angle encoder), which like the first rotational pickup has high pulse rate for each measurement operation one respective start pulse and end pulse of one of these two pickups is utilized in order, with corresponding pulses of the other of the pickup, to calculate the diameter of the roll.