by Maximous @ instructables.com:
This tutorial provides a guide on how to set up an Arduino to measure the capacitance of a capacitor. This can be useful if the capacitor is unlabeled or if it is self-built.
Capacitance is an object’s ability to store an electric charge. Reasonably, this object is referred to as a capacitor. A capacitor that stores this charge in an electric field between two conductive plates is known as a parallel plate capacitor.
Measure Capacitance with Arduino – [Link]