A resource explaining how the strength of a magnetic field drops off over distance.
| Distance, x | Field at Distance x |
|---|---|
| 0.063 | 2,690 |
| 0.125 | 2,320 |
| 0.188 | 1,970 |
| 0.250 | 1,660 |
| 0.313 | 1,390 |
| 0.375 | 1,160 |
| 0.438 | 970 |
| 0.500 | 810 |
| 0.563 | 680 |
| 0.625 | 580 |
| 0.688 | 490 |
| 0.750 | 420 |
| 0.813 | 360 |
| 0.875 | 310 |
| 0.938 | 270 |
| 1.000 | 240 |
How Does a Magnet’s Strength Drop Off Over Distance?
The strength of a magnetic field drops off roughly exponentially over distance. Here is an example of how the field (measured in Gauss) drops off with distance for a Samarium Cobalt Grade 18 disc magnet which is 1″ in diameter and 1/2″ long.
What is the equation for field strength relative to distance?
For a circular magnet with a radius of R and Length L, the field at the centerline of the magnet a distance X from the surface can be calculated by the following formula (where Br is the Residual Induction of the material):
There are additional formulae that can be used to calculate the field from a rectangular magnet and magnets in other configurations, but the formulae get too long and complex looking to include here!