Magnetic Flux Converter
Same value in every unit
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Flux and flux density are not the same quantity
Most mistakes here start by treating weber and tesla as swappable. They are not. A weber is total flux, the whole amount of magnetic field crossing a surface. A tesla is flux density, how much field is packed into each square metre. One tesla is one weber per square metre, so you cannot get from one to the other without knowing an area.
The step is a multiplication, not a conversion. A uniform 0.2 T field crossing a 0.05 m² pole face carries 0.01 Wb. Tilt that surface and the flux falls with the cosine of the angle between the field and the surface normal; edge-on it reaches zero while the field itself is unchanged. If your number came off a gaussmeter or a magnet datasheet, it is almost certainly a density, and you need the area before this converter is any use.
Why a weber is also a volt-second
Faraday's law says the magnitude of the voltage induced in one turn equals the rate at which the flux through it changes. Flux changing at one weber per second induces one volt, so the weber is dimensionally a volt-second. That is why the weber and the volt-second sit on this page with a factor of 1: they are the same unit, named for different jobs.
This is not a curiosity. One volt held for one millisecond across a single turn shifts the flux by one milliweber, and inductor and transformer cores are rated in volt-seconds precisely because that figure says how far the core can swing before it saturates.
Maxwell, gauss and the older CGS units
The maxwell is the CGS flux unit, still common in older magnet and electrical-machine literature, and it is small: 10⁻⁸ Wb, so everyday figures run into the millions of maxwells. Its density partner is the gauss, one maxwell per square centimetre. The unit pole is older again. The total flux leaving a CGS unit pole is 4π maxwells, spread over the full solid angle of a sphere, which is exactly where this page's 1.256637 × 10⁻⁷ Wb factor comes from. It is geometry, not a measured constant.
Useful anchors
- A 1 T field through 1 m² is 1 Wb; through a 10 cm × 10 cm face it is 10 mWb
- 1 Wb is one hundred million maxwells, and 1 mWb is 100,000 maxwells
- Earth's field runs roughly 25–65 µT depending on location; at 50 µT that is about 50 µWb through a one-square-metre loop held square to it
- The magnetic flux quantum is about 2.07 × 10⁻¹⁵ Wb, the step size seen in superconducting loops and SQUIDs
- A CGS unit pole emits 4π Mx in total, about 0.126 µWb
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Frequently Asked Questions
A weber measures total magnetic flux, while a tesla measures flux density, which is flux spread over an area. One tesla is one weber per square metre, so moving between them requires the area of the surface the field passes through. A uniform 0.5 T field through a 0.02 m² pole face is 0.01 Wb of flux. Tesla is not listed on this converter for that reason: there is no fixed number that turns one into the other.
Because of Faraday's law: flux changing at one weber per second through a single turn induces exactly one volt. Rearranged, one volt sustained for one second across a single turn corresponds to a one-weber change of flux, so the volt-second and the weber are the same unit under two names. Coil and core ratings are often quoted in volt-seconds because that form says directly how long a given voltage can be applied before the core saturates.
Multiply the flux density in tesla by the area in square metres, using only the component of the field perpendicular to that area. A uniform 1.2 T field crossing a flat 0.03 m² pole face gives 0.036 Wb. If the surface is tilted relative to the field, multiply by the cosine of the angle between the field and the surface normal. Without an area the conversion is undefined.
One hundred million. The maxwell is the CGS unit of magnetic flux and equals 10⁻⁸ weber, so one weber is 10⁸ maxwells and one milliweber is 100,000 maxwells. It turns up mainly in older magnet and electrical-machine texts, usually alongside the gauss, which is one maxwell per square centimetre.
The unit pole comes from CGS magnetostatics: an isolated magnetic pole of unit strength. The total flux emerging from it is 4π maxwells, because the flux spreads out over the full solid angle of a sphere. In SI that is 4π × 10⁻⁸ Wb, about 1.256637 × 10⁻⁷ Wb, so the awkward-looking factor on this page is pure geometry rather than a measured constant.
No. Gauss is a unit of flux density, the CGS counterpart of the tesla, and one gauss is 10⁻⁴ tesla. The CGS flux unit is the maxwell, and one gauss is one maxwell per square centimetre. If a meter reads in gauss you are holding a density figure, so either convert it to tesla or work out the flux by multiplying by the area it passes through.