Magnetic Units

The overall magnitude of a magnetic field is measured in units called webers, abbreviated Wb. One weber is mathematically equivalent to one volt-second (1 V . s). For weaker magnetic fields, a smaller unit, called the maxwell (Mx), is used. One maxwell is equal to 0.00000001 (one hundredmillionth) of a weber, or 0.01 microvolt-second (0.01 μV  s).

The flux density of a magnetic field is given in terms of webers or maxwells per square meter or per square centimeter. A flux density of one weber per square meter (1 Wb/m2) is called one tesla (1 T). One gauss (1 G) is equal to 0.0001 T, or one maxwell per square centimeter (1 Mx/cm2). In general, as the electric current through a wire increases, so does the flux density near the wire. A coiled wire produces a greater flux density for a given current than a single, straight wire. And the more turns in the coil, the stronger the magnetic field will be.

Sometimes, magnetic field strength is specified in terms of ampere-turns (At). This is actually a unit of magnetomotive force. A one-turn wire loop, carrying 1 A of current, produces a field of 1 At. Doubling the number of turns, or the current, doubles the number of ampere-turns. Therefore, if you have 10 A flowing in a 10-turn coil, the magnetomotive force is 10 × 10, or 100 At. Or, if you have 100 mA flowing in a 100-turn coil, the magnetomotive force is 0.1 × 100, or 10 At. (Remember that 100 mA = 0.1 A.)

A less common unit of magnetomotive force is the gilbert (Gb). This unit is the equivalent of 0.796 At. Conversely, 1 At = 1.26 Gb.