Units of B Field: Tesla, Gauss & Magnetic Flux

This page explains the units used for the magnetic flux density B field: the tesla (T) in the SI system and the gauss (G) in the CGS system. You enter a value in either unit and get the equivalent in the other, plus the corresponding magnetic flux in webers or maxwells for a given area. The calculator below converts between tesla and gauss, and also computes flux when you provide an area.

Formula

The conversion between tesla and gauss is a fixed factor:

• 1 T = 10,000 G (exactly, by definition)
• 1 G = 0.0001 T (or 10�� T)

Magnetic flux (Φ) is the product of the B field and the area perpendicular to it:

Φ = B × A

• Φ = magnetic flux in webers (Wb) when B is in tesla and A is in square meters
• B = magnetic flux density in tesla (T)
• A = area in square meters (m²)

If you use gauss and square centimeters, flux is in maxwells (Mx), where 1 Wb = 10� Mx.

Worked Example

Using the defaults: B = 1 T, area = 1 m².

1. Convert to gauss: 1 T × 10,000 = 10,000 G
2. Compute flux: 1 T × 1 m² = 1 Wb

The calculator shows the same results: 10,000 G and 1.00 Wb.

What Is the B Field?

The B field (magnetic flux density) describes the strength of a magnetic field in terms of the force it exerts on moving charges and the flux it produces through a surface. It is one of two ways to describe magnetic fields; the other is the H field (magnetic field strength), which is related to B by the permeability of the medium: B = μH.

The SI unit of B is the tesla (T), named after Nikola Tesla. One tesla is defined as one weber per square meter: 1 T = 1 Wb/m². In base SI units, 1 T = 1 kg/(s²·A).

The CGS unit is the gauss (G), named after Carl Friedrich Gauss. It is still used in some fields like geophysics and magnetometry. The conversion is exact: 1 T = 10,000 G.

How to Choose the Right Unit

Use tesla for most scientific and engineering work, especially in physics, electrical engineering, and MRI (magnetic resonance imaging) where fields are typically 1–3 T. Use gauss when working with older literature, geomagnetism (Earth’s field is about 0.5 G), or hobbyist magnets (often rated in gauss).

Also note the difference between B (flux density) and H (field strength). H is measured in amperes per meter (A/m) in SI and oersteds (Oe) in CGS. Do not confuse gauss (B) with oersted (H).

Common Mistakes and Misconceptions

• Confusing B and H: B is the total field inside a material, H is the applied field. They have different units.
• Using the wrong conversion factor: 1 T = 10,000 G, not 1,000. The factor comes from the CGS base units (cm, g, s).
• Forgetting area orientation: Flux is maximum when the area is perpendicular to the field; if the area is tilted, you must use the perpendicular component.
• Mixing systems: When using the flux formula, keep B and A in the same unit system (SI or CGS) to get the correct flux unit.

Practical Examples of B Field Values

• Earth’s magnetic field at the surface: ~25–65 μT (0.25–0.65 G)
• A typical refrigerator magnet: ~0.001 T (10 G)
• A strong neodymium magnet: ~1.2 T (12,000 G)
• MRI machine: 1.5–3 T (15,000–30,000 G)
• Neutron star: ~10� T (10¹² G)

Limits of This Calculator

This calculator only converts between tesla and gauss and computes flux for a uniform field perpendicular to a flat area. It does not account for field gradients, non-uniform fields, or the effect of materials (permeability). For real-world applications, you may need to measure the field with a gaussmeter or use simulation software.

Frequently Asked Questions

What is the difference between B and H fields?

B (magnetic flux density) is the total field including the magnetization of the material; H (magnetic field strength) is the field produced by free currents alone. They are related by B = μH, where μ is the permeability. In a vacuum, μ = μ₀ = 4π × 10�� H/m.

Why is the gauss still used if tesla is the SI unit?

Because many older instruments, textbooks, and industries (like geophysics and some magnet manufacturers) still use CGS units. The gauss is a convenient size for small fields, while the tesla is often too large for everyday measurements.

How do I convert gauss to tesla?

Divide the gauss value by 10,000. For example, 500 G = 500 / 10,000 = 0.05 T.

What is a weber?

A weber (Wb) is the SI unit of magnetic flux. One weber is the flux that produces an electromotive force of 1 volt in a one-turn loop if the flux changes uniformly to zero in one second. In terms of B and area, 1 Wb = 1 T·m².

Is the B field the same as magnetic field strength?

No. In everyday language, “magnetic field� can refer to either B or H. In physics, B is called magnetic flux density and H is called magnetic field strength. They have different units and meanings.

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in b | B field | T | 1 | 0
in a | Area | m² | 1 | 0
out bg | B in gauss | G | b * 10000 | 0
out flux | Magnetic flux | Wb | b * a | 2