Overview
Electrical and magnetic quantities span an unusually wide range of scales — a coin-cell battery's current is measured in microamps, while a lightning bolt carries tens of thousands of amps; a hobbyist's capacitor is rated in picofarads, while a Faraday-scale problem deals in whole farads. This guide walks through the core electrical and magnetic units you're likely to run into — current, voltage, resistance, charge, conductance, capacitance, inductance, and the three main magnetic quantities — and shows how each converts to its most commonly confused neighbor.
Most of these units relate to each other by exact, defined conversion factors (not approximations), which makes them straightforward to convert precisely once you know the right multiplier. Where a CGS-era unit like the gauss, abvolt, or gilbert is still involved, that's called out explicitly, since these appear more often in older textbooks and specific engineering fields than in everyday use.
Two habits make electrical unit conversion less error-prone. First, always convert to a single consistent prefix before doing arithmetic — mixing a µF value with an nF value in the same formula is one of the most common sources of design errors in hobby electronics. Second, remember that SI prefixes (milli, micro, nano, kilo, mega) apply consistently across all of these quantities, so once you're comfortable converting mA to A, the same logic carries over to mV-to-V, mF-to-F, and mH-to-H without needing to relearn the pattern for each unit.
Step 1: Convert Electric Current (Amps, Milliamps, and Beyond)
Current is the rate of charge flow, measured in amperes (A), and the practical range is enormous: a smartwatch draws a few milliamps, a household circuit breaker trips around 15–20 A, and an arc-welding machine can draw over 200 A. The base SI relationships are simple powers of ten — 1 A = 1,000 mA = 1,000,000 µA = 0.001 kA — but older CGS-electromagnetic units occasionally appear, where 1 abampere equals 10 A and 1 statampere equals about 3.336 × 10⁻¹⁰ A. The Electric Current Converter covers the full range from nanoamps to kiloamps, plus these legacy CGS units, so you can move between a datasheet's µA rating and a breaker's amp rating without manual scientific notation. This matters in practice whenever you're sizing a fuse or breaker against a component's rated draw — a mismatch of even one decimal prefix between a spec sheet and a wiring diagram can lead to an undersized protective device.
Step 2: Convert Electric Potential (Voltage)
Voltage, or electric potential difference, is measured in volts (V), with everyday devices spanning from a 1.5 V AA battery to a 400 kV+ high-voltage transmission line. Millivolts (mV) show up in sensor outputs and biosignals like ECG readings, while kilovolts (kV) describe power transmission and CRT displays. The CGS unit abvolt is defined so that 1 V = 10⁸ abvolts, while the statvolt (used in electrostatic CGS contexts) equals about 299.79 V — both are rare outside specialized physics work. The Electric Potential Converter moves between µV, mV, V, and kV instantly, which is useful when comparing a microcontroller's ADC reference voltage against a mains-level measurement. It's also worth remembering that voltage is always measured as a difference between two points, so a "voltage" reading only makes sense relative to a stated reference — ground, for instance, or the negative terminal of a battery.
Step 3: Convert Electric Resistance (Ohms)
Resistance, measured in ohms (Ω), determines how much a component opposes current flow under Ohm's Law (V = IR). A typical resistor in a hobby circuit might be rated at 220 Ω or 10 kΩ, while insulation resistance testing on cables is often specified in megohms (MΩ) — a factor of a million apart. Because resistor color-code values and multimeter readings frequently land in different unit prefixes, the Electric Resistance Converter converts cleanly between mΩ, Ω, kΩ, MΩ, and GΩ so you can match a component's marked value against a measured one without recounting zeros.
Step 4: Convert Electric Charge (Coulombs, Amp-Hours, and Elementary Charge)
Charge, measured in coulombs (C), is the quantity current moves per unit time (1 C = 1 A × 1 s). Battery capacity is more commonly expressed in amp-hours (Ah) or milliamp-hours (mAh) — a 3,000 mAh phone battery holds 3,000 × 0.001 × 3,600 = 10,800 coulombs of charge. At the smallest scale, the elementary charge (the charge on a single electron or proton) is exactly 1.602176634 × 10⁻¹⁹ C by SI definition, and the Faraday constant — one mole of elementary charges — is 96,485 C/mol, a value used constantly in electrochemistry. The Electric Charge Converter covers all of these, from single-electron charge up through amp-hour battery ratings.
Step 5: Convert Electric Conductance (Siemens and Mho)
Conductance is the reciprocal of resistance — how easily current flows through a component — measured in siemens (S), where 1 S = 1/Ω. A 100 Ω resistor has a conductance of 0.01 S, and a 10 Ω resistor has a conductance of 0.1 S. The older unit name mho (ohm spelled backward) is numerically identical to the siemens and still appears in some RF and vacuum-tube-era literature. The Electric Conductance Converter converts between mS, S, kS, and mho directly, and is the natural companion to the resistance converter when you need to flip a resistance spec into a conductance value for a filter or amplifier design calculation.
Step 6: Convert Capacitance (Farads Down to Picofarads)
Capacitance measures a component's ability to store charge per volt, in farads (F) — but a farad is such a large unit that virtually no discrete capacitor is rated anywhere near one. Ceramic capacitors on a circuit board are typically in the picofarad (pF) to nanofarad (nF) range, electrolytic capacitors in the microfarad (µF) range, and only supercapacitors approach whole farads. Since 1 F = 10⁶ µF = 10⁹ nF = 10¹² pF, a stray reading of "100n" on a component (100 nF) is easy to misplace by several orders of magnitude if converted by hand. The Capacitance Converter handles the full pF-to-F range along with the CGS abfarad (1 abfarad = 10⁹ F).
Step 7: Convert Inductance (Henries, Millihenries, Microhenries)
Inductance, in henries (H), describes how strongly a coil resists a change in current. Power supply inductors are commonly rated in millihenries (mH), RF and signal inductors in microhenries (µH), and very small PCB-trace inductances in nanohenries (nH) — a range spanning nine orders of magnitude from nH to kH. Because 1 H = 1,000 mH = 1,000,000 µH = 1,000,000,000 nH, mixing up a µH and mH value in a switching power supply design can change the calculated ripple current by a factor of 1,000. The Inductance Converter covers this entire range so component values from different datasheets can be compared on the same scale.
Step 8: Convert Magnetic Field Strength (Tesla and Gauss)
Magnetic flux density (commonly called magnetic field strength in casual use) is measured in tesla (T) in SI and gauss (G) in CGS, related by an exact factor: 1 T = 10,000 G. Earth's magnetic field at the surface is about 25–65 microtesla (0.25–0.65 gauss), a refrigerator magnet is roughly 0.005 T (50 G), and an MRI machine operates at 1.5–3 T. Because consumer and hobbyist magnet specifications are often given in gauss while scientific and medical equipment uses tesla, the Magnetic Field Converter bridges the two systems along with the equivalent SI unit weber per square metre (Wb/m², identical to tesla).
Step 9: Convert Magnetic Flux (Weber and Maxwell)
Magnetic flux — the total magnetic field passing through a given area — is measured in webers (Wb) in SI and maxwells (Mx) in CGS, with 1 Wb equal to exactly 100,000,000 (10⁸) Mx. A small bar magnet might produce a flux on the order of a few thousand maxwells through a nearby loop, a minuscule fraction of a single weber, which is why maxwells remain the more practically-sized unit for small permanent magnets even though webers are the SI standard. The Magnetic Flux Converter converts between Wb, mWb, µWb, and Mx so magnet datasheets specified in either system can be compared directly.
Step 10: Convert Magnetomotive Force (Ampere-Turns and Gilberts)
Magnetomotive force — the magnetic equivalent of voltage, describing the "push" that drives magnetic flux through a circuit — is measured in ampere-turns (At) in SI and gilberts (Gb) in CGS. The two relate by a factor involving 4π: 1 At ≈ 1.2566 Gb (equivalently, 1 Gb ≈ 0.7958 At). This quantity comes up in transformer, solenoid, and electromagnet design, where the magnetomotive force equals the number of coil turns multiplied by the current through them. The Magnetomotive Force Converter converts between At, kAt, and Gb, useful when working from an older coil-winding reference that specifies gilberts. Because it depends on turn count rather than wire gauge or voltage, two very different coils can have the same magnetomotive force if their turns-times-current products match, which is why this unit — rather than voltage or current alone — is the standard way electromagnet designs are specified and compared.
Key Terms
- Ampere (A) — the SI base unit of electric current, equal to one coulomb of charge passing a point per second
- Ohm's Law — the relationship V = IR connecting voltage, current, and resistance in a circuit
- Tesla (T) — the SI unit of magnetic flux density, equal to 10,000 gauss
- Farad (F) — the SI unit of capacitance; most real components are rated in picofarads to microfarads
- Henry (H) — the SI unit of inductance, describing a coil's opposition to changing current
- Coulomb (C) — the SI unit of electric charge, equal to the charge moved by one amp flowing for one second
- Siemens (S) — the SI unit of electrical conductance, the reciprocal of resistance in ohms
- CGS System — the centimetre-gram-second unit system that produced units like the gauss, maxwell, and gilbert, still used in some physics and electromagnetism contexts