How is the strength of a magnetic field measured?

[TheAnt]

I was wondering at what point the strength of the magnetic of a magnet was mea. I assume it would not be the origin of the field which would be inside the magnet and not the side of the magnet itself as the value would be dependant of the size of the magnet.
Is there a standard of where to measure the field eg. 1 m away from the ce ter of the magnet?
Thank you

 

[CWatters]

My understanding is that permanent magnets are measured in a machine that effectively has a "keeper" between the poles. The flux in the "keeper" is the specified "strength" of the magnet. It's the maximum magnetic flux the magnet can produce. When the "keeper" is removed the flux is free to spread out, essentially becoming less concentrated. So if you try to measure the flux in the air at some distance from a pole you will get a lower value.

I found..

http://www.first4magnets.com/tech-c.../how-is-the-strength-of-a-magnet-measured-i81

Selected extracts...

Remanence, measured in Gauss, is described as the magnetism that is left in a magnet, after the removal of the external magnetic force applied to magnetise it.

The remanence value of a magnet is the flux density held by the magnet whilst it is in a closed circuit. When the magnet is removed from the hysteresis graph testing machine, it is no longer in a closed circuit and is considered as open circuit. The magnetism falls instantly to a much lower level and this value depends on the ratio between the surface area and it's relative magnetic length.

 

[gre_abandon]

You can measure magnetic field through Hall effect. Suppose you have a piece of conductor of square shape with the four edges labeled A,B,C,D. If you apply a voltage across A,C there be a current. Now if you place this piece of material into magnetic field which will cause the charges in the material to deflect, there will be a voltage across B,D. By measuring the voltage across B,D one knows the strength of the magnetic field.