I am trying to calculate the magnetic field (in tesla/gauss) of an electromagnet that is very small and has very few windings. For example 12 windings over 0.003 meters. I know this is not going to produce a very strong field, but I would like to pulse a strong current through the coil very briefly to make it stronger. I have found an number of sources listing the formula for the calculation of magnetic field strength -
$$B = permeability * \rho * I= (μ * μ0)*(number of turns/core length)*I$$
My question is
can this formula be applied to my electromagnet design?
Does the size and low number of windings on my electromagnet mean this formula is not valid?
Is there any other way I can calculate/estimate magnetic field?