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These are two related but different quantities that are easy to confuse. Magnetic flux density (B), measured in Tesla (T) in SI units or Gauss (G) in the older CGS system, describes how concentrated a magnetic field is at a point — like the strength of a magnet's field right next to its surface. Total magnetic flux (Φ), measured in Weber (Wb), is that flux density multiplied by the area it passes through: Φ=B×A. Flux density tells you "how strong," while total flux tells you "how much" is passing through a specific surface.
| Quantity | Unit | Relationship |
|---|---|---|
| Flux density (B) | Tesla (T) or Gauss (G) | 1 T = 10,000 G |
| Total flux (Φ) | Weber (Wb) | Φ = B×Area (Wb = T×m²) |
| Earth's magnetic field | ∼0.25–0.65 G (25–65 µT) | varies by location |
| Common fridge magnet | ∼50 G (5 mT) | |
| MRI scanner | 1.5–3 T (15,000–30,000 G) |
Multiply by 10,000: e.g. 1.5 T = 15,000 G. This is an exact conversion between the SI (Tesla) and CGS (Gauss) systems.
Tesla measures flux density (field strength per unit area, like intensity at a point), while Weber measures total flux (flux density multiplied by the area it passes through). One Weber equals one Tesla acting over one square metre.
Roughly 0.25-0.65 Gauss (25-65 microtesla) at the surface, varying by location — strongest near the magnetic poles and weakest near the magnetic equator.
Around 50 Gauss (5 millitesla) at its surface for a common flexible fridge magnet, though small rare-earth (neodymium) magnets can be dramatically stronger, sometimes exceeding 5000 Gauss (0.5 Tesla).
Clinical MRI scanners commonly operate at 1.5 Tesla or 3 Tesla (15,000-30,000 Gauss), tens of thousands of times stronger than Earth's natural field, which is why MRI rooms have strict metal-object safety protocols.
Gauss (CGS system) was historically dominant, especially in the US and in older/legacy documentation, while Tesla (SI system) is now the international scientific standard — many modern datasheets, especially outside the US, use Tesla or millitesla exclusively.
Multiply the flux density (B, in Tesla) by the area it passes through (in square metres): Φ=B×A, giving flux in Weber. This assumes the field is uniform and perpendicular to the surface; angled fields require multiplying by the cosine of the angle as well.
It is a sensor that measures magnetic flux density directly, commonly used for position/proximity sensing and current measurement (via a conductor's magnetic field). Sensitivity and range specifications are typically given in Gauss or millitesla/microtesla.
Transformer and inductor cores have a maximum flux density (Bmax, in Tesla) before the core material saturates and loses its useful magnetic properties — core datasheets specify this saturation flux density, which directly limits how much voltage-time product the core can safely support, as used in the Transformer Turns (Faraday) calculator.
Yes, the same 10,000× ratio applies at any prefix scale — for example, 1 milligauss = 0.0001 microtesla×... more directly: 1 microtesla = 10 milligauss, since the base Tesla-to-Gauss ratio of 10,000 is preserved regardless of which metric prefix is used on either side.
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