Ever get a simple question that leads you down a rabbit hole? A friend of mine asked me "how much stronger are rare earth magnets than regular iron magnets", and I was given pause for thought, since I realized that I didn't really know much about how the relative "strength" of magnets are measured. I can now assure you that googling for "magnet" or "rare earth magnet" is the path to madness and pain. Wikipedia's content is useful, but reading the entry on Oersted requires more physics than I remember. The above search for data did seem to indicate that different materials do make stronger magnets. I was not suprised. But various comparatives of magnetic strength have apparently unrelated data: A "small" magnet, a "refrigerator" magnet, etc. I came away wondering "what DO we mean when we talk about how strong a magnet is", and I came up with two organic ways of thinking about it: Suppose you had two cubes that were magnetic, and they were joined at their face. The amount of force required to separate them (probably divided by the area they were joined at) would indicate how strong the magnets were Suppose I had a long cylindrical bar magnet. I take a loop of wire, move it 1 meter along the magnet, and measure how many coulombs of current I drove through the circuit, modified by the resistance of the wire. Convinced now that there is such a thing as "how strong is a magnet", that materials can make a specific difference, and that this is probably not related to size or configuration, I proceed with my question: Presuming maximum "magnetization" of the material and identical physical configuration, what is the relative magnetic strength of: A lodestone (Fe3O4) An iron magnet (Fe) A Nd2Fe14B magnet Anyone have real (or computable) data? -Jeff P.S. This seems like kind of a noob question, but some cursory searches didn't give me any clear answers.