Magnetic field strength is a measure of the intensity of a magnetic field, given in teslas (T), the standard unit. One tesla is equal to one weber per square meter, where one weber is the equivalent per second that is required to induce an electromotive force of one volt. Another way to define a tesla is that a magnetic field of 1 tesla must exert force of 1 newton on a wire of 1 meter carrying 1 ampere of current. This is a lot of force for a magnetic field to exert, as a newton is the force necessary to accelerate a 1 kg weight at 1 meter per second squared.
If all that sounds complicated, people can just think of magnetic field strength in teslas by reference to known field strengths. For instance, the Earth's magnetic field is equivalent to 1/30,000th of a tesla. Still, this is enough for birds to navigate by and to keep a compass hand pointed north. The magnetic field of Jupiter, the largest planet in the solar system, is about ten times stronger than Earth's, or 1/3,000th of a tesla. This is caused by charge circulating through metallic hydrogen in its interior.
Though the magnetic field strength of planets is relatively small, much stronger magnetic fields can be generated through artificial means. A typical loudspeaker magnetic generates a strength of 1 to 2.4 teslas. The magnetic field necessary to levitate a frog is about 17 teslas. The strongest electromagnets, which make use of superconductors, measure approximately 20 teslas. The strongest continuous magnetic field yet generated is 45 teslas, at Florida State University's National High Magnetic Field Laboratory in Tallahassee, while the strongest pulsed magnetic field obtained non-destructively was 100 teslas at the Los Alamos National Laboratory. By generating a magnetic field with an explosively pumped flux compression generator, researchers have been able to achieve a short-lived magnetic field of 2,800 teslas.