According to AllAboutCircuits.com, electrical resistance, measured in Ohms, is essentially electrical friction encountered by electrons as they move through a conductor. Ohms are typically symbolized by the Greek letter omega. The easiest way to measure resistance in a circuit is to use an ohmmeter or a multimeter. Most electricians will use a multimeter as it allows them to measure different things with the same instrument. If you are planning on doing any electrical work in your house it's a good idea to have solid grasp on using an ohmmeter.
Things You'll Need
An ohmmeter or multimeter
Red and black electrical leads
Select the ohms setting on your multimeter and set it to the highest resistance range available. Some models will auto-set the range for you. If you are using an ohmmeter, set it to the highest resistance range.
Plug the black lead into the socket labeled "Com" on your meter. Plug the red lead into the socket marked by the Greek letter omega.
Touch the ends of the two leads together. If your meter is properly functioning the display should read 0.0. It may read a slight bit higher, as the leads themselves have resistance, but if it reads over 0.3, you may have a defective meter.
Touch each the end of each lead to the end of the wire you wish to measure. Touch the leads to the wire at the same time to complete a circuit. The meter should display a reading of the resistance in ohms of the wire.
Make a note of the reading and adjust power as necessary to ensure proper functionality of the circuit.
Resistance is not usually measured across a complete circuit, rather it should be measured across each potential component of the circuit.
Never measure resistance across a live, powered circuit. Doing so may damage your meter and even cause personal injury.