Overview
Electromagnetic field and charge density quantities rank among the least commonly discussed units in everyday engineering, but they're essential in specific disciplines: antenna design, electromagnetic compatibility testing, semiconductor fabrication, and power transmission, where getting them right decides whether a design meets a safety standard or a simulation matches real-world behavior. This guide covers converters for these field and density quantities, which are easy to mix up given how similar their names sound despite describing genuinely different physical concepts.
The unit systems here span SI, CGS, and some field-specific conventions that predate both, so accurate conversion, rather than approximate mental math, matters more here than in most other unit categories. A factor-of-ten or factor-of-4ฯ error is common and easy to miss without a dedicated tool.
Step 1: Convert Electric Conductivity and Resistivity
The Electric Conductivity Converter and Electric Resistivity Converter handle these reciprocal quantities: conductivity (siemens per meter) measuring how easily a material carries current, resistivity (ohm-meters) measuring how strongly it resists. Materials datasheets in different fields tend to favor one or the other by convention. Resistivity shows up more often in semiconductor and geophysical contexts, conductivity more often in electrolyte chemistry and general materials science.
Step 2: Convert Electric Field Strength
The Electric Field Strength Converter handles volts-per-meter measurements describing the force per unit charge at a point due to a nearby electric field, distinct from voltage, which measures potential difference between two points rather than field intensity at a single point. This distinction matters in high-voltage engineering and in safety standards, which specify maximum allowable field strength near power infrastructure rather than a voltage limit alone.
Step 3: Convert Magnetic Field Strength (H-field)
The Magnetic Field Strength Converter handles the magnetizing force (amperes per meter) applied to a material, distinct from magnetic flux density (Tesla or Gauss, the B-field), which describes the resulting field within the material. The two connect through the material's magnetic permeability, but the relationship turns nonlinear in ferromagnetic materials like iron. That's exactly why keeping H-field and B-field conversions separate, rather than treating them as interchangeable, matters for accurate electromagnetic modeling.
Step 4: Convert Linear, Surface, and Volume Charge Density
Electric charge distributed across different geometries needs different units. The Linear Charge Density Converter handles charge along a line or wire (coulombs per meter), the Surface Charge Density Converter handles charge across a two-dimensional surface (coulombs per square meter), and the Volume Charge Density Converter handles charge distributed through three-dimensional space (coulombs per cubic meter). Converting between these dimensional categories, surface to volume, say, requires an additional physical calculation, typically multiplying by a thickness or other geometric factor, beyond the unit conversion itself.
Step 5: Convert Linear and Surface Current Density
The Linear Current Density Converter and Surface Current Density Converter handle current distributed along a line, such as a thin wire or sheet edge, versus across a two-dimensional conducting surface, respectively. These distinctions matter most in antenna and waveguide analysis, where current distribution across a surface, rather than a simple point-to-point current value, determines the device's radiation and impedance characteristics.
Step 6: Know When to Reach for CGS Versus SI
Many of these quantities still appear in Gauss, oersted, and other CGS-derived units in geophysical data and older electromagnetics literature, even though SI is the standard in most modern engineering work. Before converting, confirm which unit system your source data actually uses. A value reported without explicit units in a mixed-convention field like magnetics is a common source of an order-of-magnitude error once it feeds into a downstream calculation expecting the other system.
Step 7: Avoid Confusing Similarly-Named Quantities
The names in this category are easy to mix up precisely because they sound alike while describing genuinely different physical setups. Surface charge density and surface current density aren't the same quantity despite sharing "surface" in the name, and neither is interchangeable with volume charge density just because both involve "charge density." Before converting a value, confirm not just the unit but the underlying physical quantity your source actually describes. Is it charge or current? Is it distributed along a line, across a surface, or through a volume? Getting the unit conversion arithmetically correct doesn't help if it's applied to a mismatched quantity in the first place.
This is also why using the specific converter for the exact quantity you need, rather than a single generic "electromagnetic converter" that tries to cover all of them, cuts the risk of accidentally selecting the wrong quantity from a long dropdown list and ending up with a technically executed but conceptually wrong conversion.
Key Terms
- H-field vs. B-field: H-field (magnetic field strength) is the magnetizing force applied to a material; B-field (magnetic flux density) is the resulting field within it, related through the material's permeability
- Resistivity vs. Conductivity: reciprocal measures of how strongly a material resists (resistivity) versus how easily it carries (conductivity) electric current
- Charge Density: electric charge measured per unit length, area, or volume, depending on the geometry of the charge distribution being modeled
- Electromagnetic Compatibility (EMC): the engineering discipline concerned with ensuring electronic devices don't interfere with each other via electromagnetic emissions, which relies directly on field strength measurements and limits