What type of magnet to use? I am asking this question to find out practical sizes of magnets, but this will be in a fictional setting.  
Say I have a person dressed in iron armor, medieval knight-style.  Are there types of magnets that weigh on the order of 500 kg or so that would be strong enough to pull the armor to it? I'm not thinking of super-strength magnets like neodymium.  Maybe a kg of force per kg of the magnet?  Sorry, I'm not really familiar enough with magnets to know how to express their strength. 
What material would such a magnet be made of? Would the costs of making such a magnet be overly inhibitive, or is a magnet of that size even feasible? 
 A: This question does not have an easy answer. Most other online calculators are based on theoretical formulas, which are notoriously inaccurate, especially for very large or very small sizes. In addition, you will find it hard to find theoretical values that work in real world situations. This is because pull force values are tested under laboratory conditions, you probably won't achieve the same holding force under real world conditions. The effective pull force is reduced by uneven contact with the metal surface, pulling in a direction that is not perpendicular to the steel, attaching to metal that is thinner than ideal, surface coatings, and other factors. 
$\textit{This information is from a trusted website, kjmagnetics.com}$
This is directly from their site: 
"Our fanatical engineers have worked long and hard in the laboratory developing our online calculators that are VERY accurate based on thousands of test cases. Our pull force and magnetic field density calculators can be found here."
This is a link to their calculator, if you want to mess around a bit.
If you are really serious, however, there is plenty of purchasable electro-magnetic simulation software out there. 
Here is a question from a previous user about some recommended software. 
Where can I find simulation software for electricity and magnets?
