Magnetic Terms & Definitions: Gauss, Tesla, Oersted, Br, HcJ & BHmax

Magnetic terminology can be confusing because permanent-magnet engineering still uses both SI and CGS units. The most important distinction is that magnetic flux density (B) and magnetic field strength (H) are related but different quantities. Understanding terms such as gauss, tesla, oersted, coercivity, remanence and BHmax makes magnet datasheets and engineering specifications much easier to compare.

1. Magnetic Flux Density (B)

Magnetic flux density, B, describes the magnetic field at a specific location. It is measured in tesla (T) in SI units and gauss (G) in CGS units. The exact conversion is 1 T = 10,000 G.

Use the Gauss-to-Tesla Magnetic Unit Converter for gauss ↔ tesla and gauss ↔ millitesla conversions.

2. Magnetic Field Strength (H)

Magnetic field strength, H, describes the applied magnetizing or demagnetizing field. It is measured in amperes per meter (A/m or kA/m) in SI units and oersted (Oe or kOe) in CGS units. Coercivity values such as HcB and HcJ are H-field quantities.

Gauss and oersted should not be treated as interchangeable units. In free space, 1 Oe corresponds to 1 G of flux density, but inside magnetic materials the relationship between B and H depends on permeability.

3. Magnetic Flux (Φ)

Magnetic flux is the total magnetic flux passing through a surface. It is measured in webers (Wb) in SI units and maxwells (Mx) in CGS units. Fluxmeters and search coils are often used when total magnetic output is more useful than a local gauss reading.

4. Magnetic Permeability (μ)

Magnetic permeability describes how a material responds to an applied magnetic field and relates B to H. High-permeability materials such as many ferromagnetic steels provide a favorable path for magnetic flux and are widely used in magnetic circuits, back iron and pole pieces.

5. Coercivity (Hc)

Coercivity describes resistance to demagnetization. Magnet datasheets commonly distinguish HcB (normal coercivity) from HcJ (intrinsic coercivity). HcJ is especially important when evaluating resistance to irreversible demagnetization from heat or opposing magnetic fields.

6. Remanence (Br)

Remanence, Br, is the residual magnetic flux density of a magnetic material after it has been fully magnetized and the magnetizing field is removed under defined test conditions. Br is a material property; it is not the same as the surface gauss measured on a finished magnet.

7. Maximum Energy Product (BHmax)

BHmax is the maximum energy product of a permanent-magnet material and is commonly expressed in MGOe or kJ/m³. The number in an NdFeB grade such as N42 or N52 approximately corresponds to its BHmax range in MGOe. For conversion, use the MGOe-to-kJ/m³ converter.

8. Hysteresis

Hysteresis describes the dependence of a magnetic material’s state on its magnetic history. A B-H or J-H hysteresis loop shows properties such as remanence, coercivity and the path the material follows during magnetization and demagnetization.

9. Curie Temperature (Tc)

Curie temperature is the temperature above which a ferromagnetic material loses its long-range ferromagnetic ordering. It should not be confused with a magnet’s maximum operating temperature: a permanent magnet can suffer unacceptable irreversible loss well below its Curie temperature.

10. Anisotropic vs. Isotropic Magnets

• Anisotropic magnets: manufactured with a preferred magnetic orientation and normally magnetized along that designed direction for higher magnetic performance.
• Isotropic magnets: do not have the same preferred orientation and can generally be magnetized in multiple directions, usually with lower magnetic performance than comparable anisotropic material.

11. Eddy Currents

Eddy currents are circulating electrical currents induced in conductive materials by changing magnetic fields. They can create heat and energy loss in motors, generators and magnetic couplings, while also being intentionally used in braking, damping and metal detection.

12. Magnetic Coupling

A magnetic coupling transfers torque or motion across an air gap or non-magnetic barrier without a direct mechanical shaft connection. Synchronous permanent-magnet couplings are widely used in sealless pumps, HVAC equipment, mixers and other systems where leakage, contamination or shaft-seal maintenance must be reduced. Coupling performance depends on pole count, magnet geometry, magnetic gap, containment-shell material, temperature and the required breakaway torque. See Magnetic Couplings for Pumps, HVAC & Sealless Drives for the engineering guide and the Magnetic Coupling Torque Calculator for preliminary sizing.

13. Magnetic Levitation & Magnetic Bearings

Magnetic levitation uses magnetic force to support or offload a moving object without normal mechanical contact. Permanent magnets can provide lift or bearing load capacity, but stable systems still require a stabilization method such as active control, induced-current effects, diamagnetic response, spin or a mechanically constrained axis. In permanent-magnet systems, the critical design variables are the working gap, force or stiffness target, magnet geometry, pole pattern, temperature and retention method. Linear Halbach arrays are commonly used where one-sided field concentration is valuable, including Inductrack-style levitation concepts. See Magnets for Magnetic Levitation & Bearings for the design guide and the Halbach Array Visualizer for field-pattern exploration.

14. Gaussmeter

A gaussmeter measures magnetic flux density, typically with a Hall-effect probe. For repeatable inspection, the probe location, orientation, air gap and temperature should be controlled. See How Gauss Measurement Works for the full measurement guide.

Magnetic Unit Conversions

For engineering and purchasing work, the most common conversions are Gauss ↔ Tesla, Oersted ↔ kA/m, MGOe ↔ kJ/m³, Maxwell ↔ Weber, and force conversions between lbf, kgf and newtons. Use the Magnetic Unit Converter to convert these values without mixing B-field, H-field and energy-product units.

Related Technical Resources

• Magnetic Unit Converter — Gauss, Tesla, Oersted, kA/m & MGOe
• Magnets for Magnetic Levitation & Bearings
• Halbach Arrays Explained
• Magnetic Couplings for Pumps, HVAC & Sealless Drives
• Magnetic Coupling Torque Calculator
• How to Read Br, HcJ & BHmax
• What Is Gauss? Measurement & Field Units
• Neodymium Grades, Properties & Temperature Limits
• Magnet Calculator & Design Tool
• Magnet Knowledge Base
• Engineering & Procurement Resource Hub
• Request Engineering or Quote Support