There are many types of magnets, and the biggest magnet is actually not the strongest. The biggest magnet in the world is the world! Like the bar magnet from Vicky's question, our planet has magnetic north and south poles, and a magnetic field. (This magnetic field is why a compass needle always points to the north.) But scientists at the University of California, Berkeley, have recently made a hybrid magnet that is 300,000 times as strong as the earth's magnetic field! The magnet, named RD-3, is only about 3 feet long, and weighs several tons.

The strongest magnet ever build is 22-foot tall and weights 34 tons. It was built in a research lab in Tallahassee and it produces a magnetic field of at least 45 Tesla.

To understand how powerful this is you have to know that the strength of a magnetic field is measured in Gauss (G) or Tesla (T).
1 Tesla = 10,000 Gauss

The magnetic field of the earth is about 1 Gauss . The strongest magnets you can buy are about 1 Tesla. (This is already 10 000 times stronger than the earth magnet). Now the strongest magnet is even 45 000 times stronger than the earth).