Gauss to Tesla: Understanding Magnetic Field Strength

From refrigerator magnets to MRI machines, learn how to convert Gauss to Tesla and measure the power of magnetic fields.

Introduction

Magnetic field strength spans an extraordinary range, from the faint field that turns a compass needle to the fields inside a neutron star. Two units cover it: the tesla, which is the SI unit, and the gauss, which is the older CGS one and still the natural choice for weak fields.

The Core Mathematics

1 tesla = 10,000 gauss

Tesla to gauss: multiply by 10,000.
Gauss to tesla: divide by 10,000.

A clean power of ten, with no awkward constant. Both units measure magnetic flux density, which is field strength per unit area, and both are named after physicists central to the subject: Nikola Tesla and Carl Friedrich Gauss.

The tesla is a very large unit for everyday purposes, which is why the gauss persists. Most fields anyone encounters are far below one tesla, and expressing them in gauss keeps the numbers readable rather than burying them in decimal places.

A Sense of Scale

Earth's magnetic field: 0.25 to 0.65 G, or 25 to 65 microtesla
Fridge magnet: roughly 50 G (5 mT)
Speaker magnet: around 1,000 to 2,000 G
Neodymium magnet at its surface: up to about 14,000 G (1.4 T)
MRI scanner: 15,000 to 30,000 G (1.5 to 3 T)
Strongest sustained laboratory magnets: around 45 T
Neutron star: up to 10⁸ T

The Earth's field is the anchor worth remembering. It is under a single gauss, which is why a compass needle needs to be delicately balanced to respond to it at all, and why a fridge magnet held nearby overwhelms it completely.

Why MRI Machines Quote Tesla

Medical imaging is where most people meet the tesla by name. A 1.5 T scanner and a 3 T scanner differ in signal strength, and the higher field generally gives better resolution or a faster scan.

These are extraordinarily strong fields, tens of thousands of times the Earth's, and they are always on. That is the reason for the strict screening before a scan: a ferromagnetic object brought into the room does not merely stick, it is pulled hard enough to become a projectile. The field strength is the specification because it governs both the image quality and the hazard.

Field Strength Falls Off Fast

One property explains most of what magnets do in practice. The field from a small magnet falls off roughly with the cube of distance, which is far steeper than light or sound.

Doubling the distance from a small magnet leaves about an eighth of the field. This is why a magnet that grips firmly through a thin sheet does almost nothing through a thick one, and why the quoted surface field of a magnet tells you very little about its effect a few centimetres away. When comparing magnets, the pull force at a stated distance is a more useful figure than the surface flux density.

Flux Density and Total Flux

A distinction worth knowing. The tesla and gauss measure flux density, the field passing through each unit of area. Total magnetic flux is a separate quantity, measured in webers in SI and maxwells in CGS.

The relationship mirrors the field units: one weber is 10⁸ maxwells, and one tesla is one weber per square metre. In practice flux density is what specifications quote, because it describes what a magnet does at a point rather than in total.

Quick Reference Conversion Table

1 G = 0.0001 T = 100 μT
10 G = 0.001 T
100 G = 0.01 T
1,000 G = 0.1 T
10,000 G = 1 T
1 T = 10,000 G
1.5 T = 15,000 G
0.5 G ≈ Earth's field

Common Mistakes Worth Avoiding

Mixing SI and CGS in one calculation

Gauss belongs to the CGS system and tesla to SI. Magnetic formulae differ between the two systems by more than a simple factor, so convert everything into one system before calculating.

Comparing surface field to rated pull

Surface flux density and holding force measure different things. A magnet with a high surface figure may still have modest pull if it is small.

Assuming field strength is uniform

It falls off steeply with distance and varies across a magnet's face, being strongest at the edges and poles.

Conclusion

Ten thousand gauss make a tesla, which makes this the simplest conversion in the physical sciences. Use gauss for the weak fields of compasses and household magnets, tesla for the strong fields of imaging and research, and remember that the field falls away with roughly the cube of distance.

Try our gauss to tesla converter for quick and accurate conversions.