The size of magnetic field is measured in units called as webers, denoted by Wb. One weber is equivalent to one volt-second mathematically. For weaker magnetic fields, a smaller unit, called as maxwell, is used sometimes. One maxwell is equal to 0.00000001 of a weber, or 0.01 microvolt-second.
The flux density of the magnetic field can be 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 which is called as one tesla. One gauss is equal to 0.0001 weber, and one maxwell per square centimeter.
Generally greater the electric current through a wire, greater the flux density near the wire. A coiled wire will generate a greater flux density than a single, straight wire. And, the more turns in the coil, the stronger the magnetic field will be.
At times, magnetic field strength is specified in terms of ampere-turns (At). This is a unit of magnetomotive force actually. A one-turn wire loop, carrying 1 A of current, produces a field of 1 At. By doubling the number of turns, or current, will double the number of ampere-turns. Thus, if you have 10 A flowing in a 10-turn coil, magnetomotive force is 10*10. Or, if you have 100 mA flowing in a 100-turn coil, the magnetomotive force is 0.1*100, or, again, 10 At.
The other unit of magnetomotive force is gilbert. Which is equal to 0.796 At.