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Tesla vs Gauss: Understanding Magnetic Flux Density Units

Magnetic strength is measured in two different systems that overlap in everyday use β€” here is how tesla and gauss relate.

Tesla: the SI unit

The tesla (T) is the SI unit of magnetic flux density, the modern scientific standard used in physics, engineering, and most current research and equipment specifications worldwide.

Gauss: the older CGS unit

The gauss (G) is the older CGS-system unit for the same quantity. It is much smaller than a tesla β€” specifically, 1 tesla equals exactly 10,000 gauss β€” which is why gauss is often more convenient for describing weaker, everyday magnetic fields.

Why both units are still around

Gauss remains common in the US and in older instrumentation and industry standards, particularly for things like permanent magnets and some medical or electronics specifications, while Tesla dominates in scientific literature and SI-based engineering worldwide.

Everyday reference points

For scale: Earth's magnetic field at the surface is roughly 25-65 microtesla (0.25-0.65 gauss), a basic refrigerator magnet is around 5 millitesla (50 gauss), and hospital MRI machines typically operate between 1.5 and 3 tesla (15,000-30,000 gauss) β€” a difference of several orders of magnitude.

Flux density vs field strength

Flux density (B, measured in tesla or gauss) and magnetic field strength (H, measured in amperes per meter or oersteds) are related but technically distinct quantities β€” in everyday conversation "magnetic field strength" usually refers loosely to flux density, but the two have different formal units and only coincide in certain conditions.

Check the unit before comparing readings

Gaussmeters and teslameters often measure the same underlying quantity but display it in different units, so checking which unit a device or spec sheet is using before comparing numbers is important β€” a "500" reading means very different things in gauss versus tesla.

Why two unit systems for the same quantity

Tesla comes from the SI system that most of science formally standardized on, while gauss comes from the older CGS system that predates it. Because gauss happens to be a convenient size for describing common, relatively weak magnetic fields, like Earth's field or small magnets, it never fully disappeared from everyday and industrial use even after Tesla became the official scientific standard.

How MRI field strength communicates capability

When a hospital advertises a "3T MRI" versus a "1.5T MRI," the tesla rating describes the strength of the machine's magnetic field, which directly affects image resolution and scan speed β€” higher field strength generally means clearer images, though it also comes with higher cost and, for some patients, additional considerations around implants and comfort.

Frequently Asked Questions

Is a magnet rated stronger in gauss automatically stronger in tesla?

Yes β€” the conversion between the two is a fixed, linear ratio (1 tesla = 10,000 gauss), unlike some unit pairs that vary by context. A magnet with a higher gauss rating will always have a proportionally higher tesla rating, since they are measuring the exact same physical quantity.

Why do some countries still print gauss values on magnets and equipment?

It is largely a matter of industry convention and legacy instrumentation, especially in the US, where gauss has historically been the more familiar unit for consumer and industrial magnet specifications, even as scientific literature has moved almost entirely to tesla.