A magnet's strength is measured in Gauss or Tesla, which indicate the strength of the magnetic flux. A Gaussmeter, also known as a magnetometer, gives a reading of the magnetic flux in units of Gauss or Tesla (a Tesla is equal to 10,000 Gauss). A gauss is equal to one newton per ampere meter, or the amount of force divided by the current and distance. The surface of the Earth has a magnetic flux of 0.5 Gauss; most magnets have a strength of about 100 Gauss.
Take the magnet to an area with no other magnetic objects (such as microwaves and computers).
Place the Gaussmeter directly on on the surface of one of the magnet's poles.
Locate the needle on the Gaussmeter and find the corresponding heading. Most Gaussmeters have a range of 200 to 400 Gauss, with 0 Gauss (no magnetic field) in the center, negative Gauss on the left and positive Gauss on the right. The further to the left or right the needle lies, the stronger the magnetic field.