What are Gauss and Tesla in relation to magnets?
Short answer: Gauss (G) and Tesla (T) are units for the strength of a magnetic field (the flux density B). 1 Tesla = 10,000 Gauss; 1 milliTesla (mT) = 10 Gauss. At the surface of a neodymium magnet you usually measure 2,000 to approx. 6,500 Gauss (0.2 – 0.65 T), depending on size, shape and grade. A higher Gauss value does not automatically mean more holding force in kg.
Converting: Gauss, Tesla and milliTesla
| Gauss | milliTesla | Tesla |
|---|---|---|
| 1 G | 0.1 mT | 0.0001 T |
| 10 G | 1 mT | 0.001 T |
| 1,000 G | 100 mT | 0.1 T |
| 5,000 G | 500 mT | 0.5 T |
| 10,000 G | 1,000 mT | 1 T |
Tesla is the official SI unit; Gauss comes from the older CGS system but is still widely used in the magnet world.
How strong are magnetic fields? Comparison
| Source | Field strength (approx.) |
|---|---|
| Earth's magnetic field (Netherlands) | 0.5 G (50 µT) |
| Fridge magnet (ferrite/rubber) | 50 – 100 G |
| Ferrite magnet, surface | 500 – 1,500 G |
| Neodymium disc magnet, surface | 2,000 – 6,500 G |
| Remanence Br of neodymium (in the material) | 11,700 – 14,800 G (1.17 – 1.48 T) |
| MRI scanner (hospital) | 15,000 – 30,000 G (1.5 – 3 T) |
Surface field is not the same as remanence
Datasheets often show a remanence (Br) of, for example, 1.4 T or 14,000 Gauss. That is a material property: the field inside a closed magnetic circuit. At the surface of a loose magnet you always measure much less, usually 20 to 50% of Br. Exactly how much depends on the ratio between thickness and diameter: a thick magnet (Ø10 x 10 mm) reaches a higher surface value than a thin one (Ø10 x 1 mm). More in what is remanence (Br)?
Why does Gauss say little about holding force?
A Gauss meter measures the field at one point. Holding force depends on the field over the entire contact surface and on how far the field reaches. A small, thick magnet can have a higher surface Gauss value than a large, thin magnet, while the large magnet holds more kilos. If you want to know what a magnet can carry, look at the holding force in kg. See how strong is a neodymium magnet?
How is it measured?
With a Gaussmeter or Teslameter with a Hall probe. The reading depends strongly on the position (centre or edge), the distance (a thick probe housing already measures at 0.5 – 1 mm) and the orientation of the probe. So only compare values that were measured in the same way.
Frequently asked questions
How many Gauss does an N52 magnet have?
The material has a remanence of 14,300 – 14,800 Gauss. At the surface of an ordinary N52 disc magnet you usually measure 3,000 to 6,500 Gauss, depending on the size.
Is 1 Tesla a lot?
Yes. That is 20,000 times the earth's magnetic field. In practice you do not reach that at the surface of a loose permanent magnet.
Is the field of a neodymium magnet harmful to people?
Static fields of this strength are not harmful to healthy people, but they are for pacemakers and ICDs. Keep at least 15 cm away, or more with large magnets, and follow the advice of the device manufacturer. Read are neodymium magnets dangerous? and magnets and electronics.
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