I have built a new electromagnet, my second one so far, in an attempt to make it better. I am trying to find its strength, whether that be in tesla, holding force (kg) or whatever other units there are, just so I can compare it with other magnets. What I have is a steel bolt wrapped with 1000+ turns of 26AWG copper wire. There are 8 AA batteries in series, giving about 12V, and a current of about 0.22A. The coil is approximately 7cm long, and has an outer diameter of approximately 1.2cm (I think the bolt is 3/8 of an inch), with 8 layers of wire. Can someone please provide me with the formula(e) required to find what I am looking for. If there are any other variables needed please let me know. Also, what are good alternatives for a bunch of AA batteries? I would like it to be portable - not connected to a powerpoint - and to have it more powerful, so more current from the batteries. Thanks for any help.