Magnetic Field Strength Converter
Instantly convert magnetic field strength with our free converter. See conversion tables, formulas, and step-by-step explanations.
Calculator
Adjust values & calculateAll Conversions
| Unit | Value |
|---|---|
| Ampere per meter (A/m) | 1.000000e+0 |
| Kiloampere per meter (kA/m) | 1.000000e-3 |
| Oersted (Oe) | 1.256637e-2 |
| Gilbert per centimeter | 1.256637e-2 |
| Ampere-turn per meter (At/m) | 1.000000e+0 |
| Ampere-turn per centimeter | 1.000000e-2 |
| Ampere-turn per inch | 2.540000e-2 |
| Milliampere per meter (mA/m) | 1.000000e+3 |
| Millioersted (mOe) | 1.256637e+1 |
Formula
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.
Last reviewed: December 2025
Worked Examples
Example 1: Solenoid Field Strength
Example 2: Material Coercivity Conversion
Background & Theory
The Magnetic Field Strength Converter applies the following established principles and formulas. Unit conversion is the process of expressing a quantity in a different unit of measurement while preserving its physical meaning. At the foundation of modern measurement lies the International System of Units (SI), which defines seven base units: the meter for length, kilogram for mass, second for time, ampere for electric current, kelvin for thermodynamic temperature, mole for amount of substance, and candela for luminous intensity. All other units, called derived units, are defined as algebraic combinations of these seven. Dimensional analysis is the principal method for performing unit conversions. By treating units as algebraic quantities that can be multiplied, divided, and cancelled, a conversion factor chain allows a value expressed in one unit to be rewritten in another without altering its physical magnitude. For example, to convert 60 miles per hour to meters per second, one multiplies by a chain of conversion factors each equal to one: (1609.34 m / 1 mile) × (1 hour / 3600 s). Metric prefixes enable compact expression of quantities across extreme ranges of magnitude. Standard prefixes span from nano (10^-9) through micro (10^-6) and milli (10^-3) up through kilo (10^3), mega (10^6), and giga (10^9), and beyond in both directions. These prefixes are strictly multiplicative and apply consistently to any SI base or derived unit. Temperature conversions require affine transformations rather than simple scaling. To convert Celsius to Fahrenheit the formula is °F = (°C × 9/5) + 32, while the conversion to the absolute Kelvin scale is K = °C + 273.15. These formulas reflect the different zero points and degree-size conventions of each scale. Significant figures govern how precision is preserved through calculations. A result should not express more precision than the least precise input value permits. In digital storage, IEEE and IEC standards distinguish between decimal prefixes (kilobyte = 1000 bytes) and binary prefixes (kibibyte = 1024 bytes), a distinction that has practical consequences for how storage capacity is reported by manufacturers versus operating systems. Unit coherence — ensuring that all quantities in an equation share a consistent unit system — is essential for obtaining correct results.
History
The history behind the Magnetic Field Strength Converter traces back through the following developments. Human beings have been measuring and comparing quantities since before recorded history. The earliest known measurement units were body-based: the cubit (the distance from elbow to fingertip), the foot, the hand, and the digit. The furlong originated as the length of a furrow a team of oxen could plow without resting. These anthropomorphic standards were practical for local use but differed between regions and kingdoms, creating persistent difficulties in trade and construction. The ancient Egyptians standardized the royal cubit at approximately 52.4 centimeters and distributed calibrated granite rods to ensure consistency across building projects, including the pyramids. Roman engineers used the mile (mille passuum, one thousand double paces) and spread these standards throughout their empire via road networks. Despite these efforts, measurement diversity persisted across medieval Europe, hampering commerce. The French Revolution created political will for radical standardization. In 1795 France officially adopted the metric system, defining the meter as one ten-millionth of the distance from the equator to the North Pole along the Paris meridian. This gave the world its first fully decimal, rationally constructed measurement system. The Metre Convention of 1875 established the International Bureau of Weights and Measures (BIPM) in Sevres, France, creating a permanent international body to maintain physical artifact standards and coordinate global metrology. For over a century, the kilogram was defined by a platinum-iridium cylinder locked in a vault near Paris. In 1999, a stark demonstration of what unit inconsistency costs occurred when NASA's Mars Climate Orbiter was lost because one engineering team used pound-force seconds while another used newton seconds. The spacecraft entered the Martian atmosphere at the wrong angle and was destroyed, at a cost of 327 million dollars. In 2019 the SI underwent its most significant revision, redefining all seven base units in terms of fixed numerical values of fundamental physical constants such as the speed of light, Planck's constant, and the elementary charge. This eliminated any reliance on physical artifacts and made the measurement system permanently stable and universally reproducible.
Frequently Asked Questions
Sources & References
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\nConvert to Oe: 4000 / 79.5775 = 50.27 Oe\nThis 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\nConvert to kA/m: 71,619.7 / 1000 = 71.62 kA/m\nThis 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.
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.
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.
References
Reviewed by Manoj Kumar, Mathematics Educator · Editorial policy