Magnetic Field Converter

Seven units across thirteen decades: tesla, millitesla, microtesla, nanotesla, kilogauss, gauss and milligauss. The conversion itself is the easy part — 1 T is 10,000 G exactly, by the definition of the CGS unit — so the value of a tool like this is mostly in seeing where a number sits. The Earth's surface field runs roughly 25 to 65 µT depending on latitude, which is 0.25 to 0.65 G; a clinical MRI runs at 1.5 or 3 T, or 15,000 to 30,000 G; the nanotesla is where geomagnetism lives, and it is still labelled γ here because the gamma was the older name for exactly the same amount.

What the tool deliberately leaves out is as important as what it contains. Every unit here measures B, the magnetic flux density. The related quantity H, the magnetising field, has its own units — amperes per metre in SI, oersted in CGS — and they are not interchangeable with these. A field of 1 Oe in vacuum does correspond to 1 G, which is exactly why the two get confused, but that correspondence holds only in vacuum: inside a material B and H differ by the permeability, which for soft iron can be thousands. So a datasheet quoting oersteds for a coercivity and one quoting gauss for a remanence are describing different quantities, and converting one to the other with the factor on this page will give you a number that means nothing.

Even the vacuum correspondence is no longer exact. When the ampere was redefined in 2019, μ₀ stopped being exactly 4π × 10⁻⁷ and became a measured quantity; it now differs from the old value by about 1.4 parts in 10¹⁰, so 1 Oe in vacuum is 0.9999999999 G rather than 1. Nothing you measure will notice, but the definition no longer closes.

Values below 0.0001 are shown in exponential form — a nanotesla in tesla reads 1.0000e-9 — and everything else to eight significant digits.