Magnetic units grouped by what they actually measure — with the conversions that exist done exactly, and the ones that do not explained rather than guessed.
Calculator
Try:
T to Oe
No conversion exists
T measures magnetic flux density (B) and Oe measures magnetic field strength (H). These are different quantities; no factor converts between them.
Everything that measures the same thing
Flux density (B) — what a field meter reads
Unit
Value
System
Note
nanotesla (nT)
1.0000e+9
SI
Geomagnetic surveys work in these. Earth’s field is tens of thousands of them.
microtesla (µT)
1.0000e+6
SI
Earth’s field at the surface is roughly 25 to 65 of these.
gauss (G)
10,000.0
CGS
Exactly a ten-thousandth of a tesla. Still standard for permanent magnets.
millitesla (mT)
1,000.0
SI
A fridge magnet at its surface is a few of these.
kilogauss (kG)
10.0000
CGS
A neodymium magnet’s remanence is around 13 of these.
tesla (T)
1.0000
SI
The SI unit. A clinical MRI runs at 1.5 or 3.
This table only ever contains one quantity, which is the design. Magnetic units come in four families — flux density, field strength, flux and energy density — and the conversions inside a family are exact while there is no conversion at all between them. A dropdown that mixed them would be the bug this page exists to name.
Why one gauss looks like one oersted
One oersted of drive produces1.0000 G1.0000e-4 T
Relative permeability1The only case where the gauss and the oersted come out numerically equal.
And your 1 T needs795,774.7 A/m10,000.0 Oe of drive
In vacuum, one oersted produces exactly one gauss — which is why generations of engineers have used the two words interchangeably. Change the material and the equality vanishes: the same one oersted produces two thousand gauss in a ferrite core. The coincidence was a choice of units, never a statement that B and H are the same thing.
Compass grades
N42 in SI334.2 kJ/m³maximum energy product, (BH)max
Field at the magnet’s surfacenot calculabledepends on shape, not on grade
A grade is an energy density, not a field. N42 means 42 MGOe, or 334kJ/m³ — a statement about how much energy the material can store per unit volume. What you would measure at the surface depends on the magnet’s shape, its length along the magnetisation axis, and exactly where the probe sits, so this tool converts the grade and declines to invent a gauss figure from it.
Something to measure against
Flux density across twenty-one orders of magnitude
Where
Tesla
Gauss
Note
Human brain, measured by SQUID
1.0e-13
1.0e-9
Magnetoencephalography, in a shielded room. A hundred femtotesla.
Interstellar space
1.0e-10
1.0e-6
Faint, and enough to shape galactic structure over long distances.
Earth’s field at the surface
5.0e-5
5.0e-1
25 to 65 microtesla depending on latitude — 0.25 to 0.65 gauss.
Fridge magnet at its surface
5.0e-3
5.0e+1
About 50 gauss. A hundred times Earth’s field, and it still falls off within centimetres.
Neodymium magnet at its surface
5.0e-1
5.0e+3
Around 5000 gauss. Its remanence is higher; the surface reads lower because of geometry.
Clinical MRI
3.0e+0
3.0e+4
Sixty thousand times Earth’s field, held stable across a room-sized volume.
Strongest continuous laboratory magnet
4.5e+1
4.5e+5
Resistive and superconducting coils together, cooled hard.
Neutron star surface
1.0e+8
1.0e+12
And a magnetar is a thousand times that again.
The gauss survives in permanent magnets and the tesla everywhere else, and the reason is visible in the two columns: Earth’s field is half a gauss and a fridge magnet is fifty, so gauss is a comfortable size for magnets. An MRI at 3 T is 30,000 gauss, at which point the tesla is the comfortable one instead.
What this converter covers
Thirteen units in four quantity groups, the permeability bridge between B and H, magnet grades in both systems, and a scale from a brain to a neutron star.
Tesla, gauss, millitesla, microtesla, nanotesla and kilogauss
Ampere per metre, kiloampere per metre and oersted
Weber and maxwell
Magnet grades in MGOe and kJ/m³
The permeability bridge from field strength to flux density, per material
Grouped by quantity Gauss is not oersted Permeability bridge SI and CGS
Free, no signup — exact by definition, not an estimate.
Updated 8 September 2026
At a glance
Formula shown
1 T = 10 000 G exactly · 1 Oe = 1000/4π A/m · B = μ₀ μᵣ H
Scenario support
Earth’s field is 0.5 G · one oersted is 1 G in vacuum and 2000 G in ferrite
Educational estimate
Planning support from the values you enter — not professional advice.
Four quantities, not one
Most unit converters for magnetism put every unit in one dropdown, and that single design decision produces most of the confusion in the field.
There are four separate quantities here, and only three of them are related at all:
What each family measures
Quantity
SI unit
CGS unit
What it describes
Flux density, B
tesla
gauss
The field that is actually there — what a meter reads
Field strength, H
A/m
oersted
The field being applied — what a current drives
Flux, Φ
weber
maxwell
Flux density times the area it passes through
Energy density
kJ/m³
MGOe
How strong a magnet material is, per unit volume
Gauss to tesla is exact — ten thousand to one, by definition — and so is maxwell to weber. Gauss to oersted is not a conversion at all. They are the CGS units of two different quantities, and putting them in one list implies a relationship that needs a material before it exists.
The calculator above groups the dropdown accordingly, and when you pick a target from a different group it tells you which two quantities you have mixed rather than returning nothing.
The coincidence that causes it
The reason experienced engineers treat gauss and oersted as interchangeable is that, in the one case they usually meet, they are numerically identical.
In vacuum, one oersted of field strength produces exactly one gauss of flux density. The CGS system was constructed so that the permeability of free space came out as 1, which makes B and H the same number in air — and air is where most measurements happen.
Put the same field into a material and the equality vanishes:
One oersted of drive, four materials
Material
Relative permeability
Flux density
Vacuum or air
1
1 gauss
Soft ferrite
2,000
2,000 gauss
Electrical steel
4,000
4,000 gauss
Mu-metal
20,000
20,000 gauss
Same drive, four different fields, four orders of magnitude apart. The one-to-one relationship was never a property of the units; it was a property of vacuum, and it is the entire reason transformers, inductors and magnetic shields work at all.
In SI the coincidence is not available to mislead anyone, because one oersted is 79.577 A/m and one gauss is 0.0001 T. The numbers no longer look alike, which is a small argument in favour of the system nobody in magnetics fully adopted.
Where the 4π comes from
Two conversions on this page are clean powers of ten and two carry a 4π, and the split is worth understanding rather than memorising.
A tesla is exactly 10,000 gauss. A weber is exactly 100,000,000 maxwell. Both are pure decimal factors, because both are the same quantity measured in metres rather than centimetres.
An oersted, though, is 1000 ÷ 4π ampere per metre — about 79.577. The 4π is there because CGS electromagnetic units were built around a point source spreading over the surface of a sphere, and the sphere’s 4π was absorbed into the unit definitions rather than kept in the equations.
SI made the opposite choice: keep the units clean and let the 4π appear in μ₀ instead. Neither is wrong, and the seam between them is exactly where a factor of 12.57 waits for anyone converting carelessly.
The same 4π shows up in the magnet grade conversion, for the same reason: one MGOe is 100 ÷ 4π kilojoules per cubic metre, or about 7.958. Rounding it to 8 is a 0.5% error, which is more than the tolerance on the grade it is describing.
A magnet grade is not a field
The N-number on a neodymium magnet is the most misread figure in the whole subject, because it looks like a strength and is not one.
N42 means a maximum energy product of 42 MGOe — about 334 kJ/m³. That is an energy density: how much magnetic energy the material can store per unit of its own volume. It is a property of the material, and it is exactly what you want when comparing one alloy against another.
What it does not tell you is the field at the surface, because that depends on the magnet’s shape. A long thin magnet and a flat disc of the same grade and the same volume have very different surface fields, and both are lower than the material’s remanence, because a real magnet has to supply its own return path through the air.
So the calculator converts the grade between MGOe and kJ/m³ and declines to produce a gauss figure from it. Getting the field at a point needs the geometry, and for anything beyond a rough disc or cylinder it needs a field solver rather than a formula.
One further caveat worth carrying: grades fall with temperature, and neodymium falls faster than most. A magnet specified at room temperature can lose a noticeable fraction of its output at 80 °C, and the letter suffixes on the grade — N42SH and so on — are exactly about that.
Which unit to use
Both systems are still in daily use, in different corners, and the division is not arbitrary.
Gauss survives in permanent magnets and in geomagnetism, because it is a comfortable size there. Earth’s field is about half a gauss; a fridge magnet is fifty; a neodymium magnet at its surface is a few thousand. Writing those in tesla means a string of decimal places or a prefix on every figure.
Tesla dominates everywhere the fields are large — MRI at 1.5 or 3, motors and transformers around 1 to 2, laboratory magnets in the tens. Here the gauss figure runs to five digits and stops helping.
Oersted and MGOe persist in the magnet industry, largely because the datasheets and the people reading them have been in those units for decades. A European datasheet will usually give kJ/m³ and kA/m alongside, and the two sets of numbers on one page are the clearest illustration of everything above.
The practical rule is to convert to SI when you are calculating and to convert back when you are talking to whoever supplied the part. Mixing them inside one calculation is where the 4π gets lost.
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The NIST guide is where the CGS-to-SI factors come from and is explicit that these units should be converted rather than mixed; the other two establish that flux density, field strength and flux are three separate quantities with three separate SI units.
Guide for the Use of the International System of Units (NIST SP 811)National Institute of Standards and Technology · verified 2026-09-08 · The conversion factors between the CGS electromagnetic units and their SI counterparts — gauss to tesla, oersted to ampere per metre, maxwell to weber — and the guidance that CGS magnetic units be converted to SI rather than mixed with them
International System of Units — units and constantsNIST Physical Measurement Laboratory · verified 2026-09-08 · The tesla, weber and ampere per metre as the SI units of magnetic flux density, magnetic flux and magnetic field strength respectively — three distinct quantities with distinct units
SI Brochure, 9th editionBureau International des Poids et Mesures · verified 2026-09-08 · That magnetic flux density and magnetic field strength are separate derived quantities related through the permeability of the medium, which is why a conversion between their units requires a material to be specified
Conversion note
The conversions within each quantity are exact and the permeability bridge is not. Relative permeability is a property of a specific material in a specific state: it varies with the field applied, with temperature, with frequency, and with how the material was processed, and for ferromagnetic materials it is not even single-valued — the same field can correspond to different flux densities depending on the material's magnetic history. The figures offered here are representative values for illustration, not design data; take those from the manufacturer's B-H curve for the grade and temperature you are using. Magnet grades are maximum energy products measured under standard conditions and decline with temperature, sometimes steeply, and the field around a real magnet depends on its geometry and on any steel near it. Nothing here addresses magnetic safety: strong magnets and MRI environments present real hazards to implanted devices, to loose ferrous objects and to fingers, and those are matters for the equipment's own safety documentation.
Published the Gauss to Tesla Converter: thirteen magnetic units grouped into four quantities -- flux density, field strength, flux and energy density -- with exact conversions inside each group and no conversions between them.
Refuses gauss to oersted, which is the conversion most people arrive wanting, and explains why: tesla and gauss measure flux density while ampere-per-metre and oersted measure field strength, and crossing between them needs a permeability rather than a factor.
Names the coincidence that causes the confusion. In vacuum one oersted produces EXACTLY one gauss, because CGS was built so the permeability of free space came out as 1 -- and the same one oersted produces two thousand gauss in a ferrite core.
Provides the bridge explicitly, with a material selector spanning vacuum to mu-metal, so the four-orders-of-magnitude spread is the output rather than a footnote.
Explains why two of the conversions are clean powers of ten and two carry a 4 pi: an oersted is 1000 over 4 pi ampere per metre, and rounding it to 79.6 loses accuracy the rest of the table does not.
States that a magnet grade is an energy density and not a field. N42 is 42 MGOe, or 334 kJ per cubic metre, and the tool converts the grade while refusing to produce a surface gauss figure, which depends on geometry.
Gives a scale from magnetoencephalography at a hundred femtotesla to a neutron star at 100 megatesla, and explains which unit is comfortable where -- gauss for permanent magnets and geomagnetism, tesla everywhere the fields are large.
Verified by 91 automated cases, asserting that every cross-quantity pair returns null AND names both quantities in its refusal, that one oersted gives exactly one gauss in vacuum and two thousand in ferrite, that the oersted and MGOe factors match 1000/4pi and 100/4pi rather than rounded decimals, and that no export produces a field from a magnet grade.
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