Magnetic Field Strength Converter
Instantly convert magnetic field strength with our free converter. See conversion tables, formulas, and step-by-step explanations.
Reviewed for accuracy by Manoj Kumar, Mathematics Educator
Magnetic Field Strength Converter
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Formula: Converted Value = Input x (From Unit Factor / To Unit Factor)
Worked example โ H = 4000 A/m = 50.27 Oe
Formula
Converted Value = Input x (From Unit Factor / To Unit Factor)
Magnetic field strength conversion uses the ampere per meter (A/m) as the base SI unit. All other units relate to A/m through fixed conversion factors. The oersted, the CGS unit, equals approximately 79.5775 A/m. Ampere-turn per meter is dimensionally identical to A/m since the turn is dimensionless.
Worked Examples
Example 1: Solenoid Field Strength
Problem:A solenoid has 500 turns, carries 2 A of current, and is 0.25 m long. Find H in A/m and oersted.
Solution:H = N * I / l = 500 * 2 / 0.25 = 4000 A/m Convert to Oe: 4000 / 79.5775 = 50.27 Oe This is the field strength inside the solenoid core.
Result:H = 4000 A/m = 50.27 Oe
Example 2: Material Coercivity Conversion
Problem:A permanent magnet has a coercivity of 900 Oe. Express this in A/m and kA/m.
Solution:H = 900 x 79.5775 = 71,619.7 A/m Convert to kA/m: 71,619.7 / 1000 = 71.62 kA/m This coercivity indicates a moderately hard magnetic material.
Result:900 Oe = 71,620 A/m = 71.62 kA/m
Frequently Asked Questions
What is magnetic field strength (H)?
Magnetic field strength, denoted H, is the measure of the magnetizing force that creates a magnetic field. The SI unit is ampere per meter (A/m). Unlike magnetic flux density (B), which depends on the medium, H represents the applied magnetizing force independent of the material. In a solenoid, H equals the number of turns times the current divided by the length (H = NI/l). It is sometimes called magnetizing field or magnetic field intensity.
How do I convert between A/m and oersted?
One oersted (Oe) equals approximately 79.5775 amperes per meter (A/m). To convert A/m to oersted, divide by 79.5775. To convert oersted to A/m, multiply by 79.5775. The oersted is the CGS unit of magnetic field strength, still widely used in magnetics and materials science. For example, the Earth magnetic field is about 0.5 Oe or approximately 39.8 A/m at the surface.
What is the difference between H-field and B-field?
The H-field (magnetic field strength, in A/m) represents the applied magnetizing force, while the B-field (magnetic flux density, in tesla) represents the total magnetic field including the material response. They are related by B = u0 * ur * H, where u0 is the permeability of free space and ur is the relative permeability of the material. In vacuum, B and H differ only by the constant u0, but in magnetic materials, the B-field can be thousands of times larger than what H alone would produce.
What are typical magnetic field strength values?
The Earth magnetic field strength at the surface is about 25-65 A/m (0.3-0.8 Oe). A typical refrigerator magnet produces about 4000 A/m (50 Oe) at its surface. Hard disk drive write heads generate around 200,000 A/m (2500 Oe). Powerful electromagnets in MRI machines operate at field strengths equivalent to millions of A/m. Industrial demagnetizers may apply fields exceeding 80,000 A/m (1000 Oe) to erase residual magnetism.
What is coercivity and how does it relate to magnetic field strength?
Coercivity is the intensity of the applied magnetic field (H) required to reduce the magnetization of a material to zero after it has been magnetized to saturation. It is measured in the same units as magnetic field strength, typically A/m or oersted. Soft magnetic materials like iron have low coercivity values of a few A/m, meaning they are easily demagnetized and are used in transformer cores and electromagnets. Hard magnetic materials like neodymium magnets have coercivity values exceeding 800,000 A/m, making them resistant to demagnetization and suitable for permanent magnets. Coercivity is a critical parameter in selecting materials for magnetic storage, motors, and shielding applications.
What is the relationship between magnetic field strength and permeability?
Permeability describes how responsive a material is to an applied magnetic field strength H. The relationship is expressed as B = mu * H, where B is the magnetic flux density, mu is the permeability, and H is the field strength. Permeability is often expressed as the product of the permeability of free space (mu0 = 4 pi times 10 to the negative 7 H/m) and relative permeability (mu_r). Vacuum and air have mu_r of approximately 1, while ferromagnetic materials like soft iron can have mu_r values in the thousands. High permeability materials concentrate magnetic flux and are used in magnetic shielding and inductor cores.
Why is the oersted unit still used alongside the SI unit A/m?
The oersted belongs to the centimeter-gram-second (CGS) system of units, which was the standard in electromagnetics for over a century before the SI system was adopted internationally. Despite the official SI recommendation to use amperes per meter, the oersted remains widely used in the permanent magnet industry, materials science, and magnetics engineering, particularly in the United States and Japan. Datasheets for permanent magnets, magnetic recording media, and hysteresis measurements frequently quote coercivity and field strength in oersted. The persistence of CGS units in these fields is largely due to historical convention and the extensive body of reference data published in oersted.
How is magnetic field strength measured in practice?
Magnetic field strength H is typically not measured directly but is inferred from measurements of magnetic flux density B using a known material's permeability or from the current and geometry of an electromagnet. In a solenoid, H is calculated from the number of turns, current, and length. Gaussmeters and teslameters measure B directly using Hall effect sensors or fluxgate probes, and H can then be derived if the material properties are known. For characterizing magnetic materials, a B-H analyzer or vibrating sample magnetometer applies known field strengths and measures the resulting flux density to map the full hysteresis loop.
What is the difference between ampere per meter and ampere-turn per meter?
Ampere per meter (A/m) and ampere-turn per meter (At/m) are dimensionally identical because the turn is a dimensionless quantity representing the number of wire loops in a coil. In practical electromagnet design, the term ampere-turn is used to emphasize that the magnetizing force depends on both the current in amperes and the number of turns in the winding. For example, a coil with 500 turns carrying 2 amperes produces 1000 ampere-turns of magnetomotive force. Dividing by the magnetic path length gives the field strength in At/m, which is numerically the same as A/m. The distinction is purely one of engineering convention rather than physical difference.
How does temperature affect magnetic field strength in permanent magnets?
Temperature significantly impacts the magnetic field strength produced by permanent magnets through a property called the temperature coefficient of remanence. As temperature increases, thermal agitation disrupts the alignment of magnetic domains, reducing the magnet's internal field strength. Ferrite magnets lose about 0.2 percent of their strength per degree Celsius, while neodymium magnets lose about 0.1 percent per degree Celsius. Above a critical temperature called the Curie point, magnetic ordering is completely destroyed and the material becomes paramagnetic. The Curie temperature is approximately 310 degrees Celsius for neodymium magnets and 770 degrees Celsius for iron. Engineers must account for these thermal effects when designing magnetic circuits for high-temperature applications.
References
Reviewed for accuracy by Manoj Kumar, Mathematics Educator ยท Editorial policy
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