All Voltage Units

How to Convert Voltage Units?

Voltage (electric potential difference) is measured in Volts, named after Alessandro Volta. Converting between voltage units uses standard metric prefixes: milli (1/1000), micro (1/1000000), kilo (1000), and mega (1000000). Our converter provides precise conversions for applications ranging from microelectronics to power transmission systems.

Frequently Asked Questions

What units does the voltage converter cover?

This converter handles the SI volt and its standard prefixed forms: nanovolt (nV), microvolt (uV), millivolt (mV), volt (V), kilovolt (kV), and megavolt (MV). The volt is the SI derived unit of electric potential difference, equal to one joule per coulomb (J/C) or one watt per ampere (W/A). All prefixes scale by exact powers of ten, so conversions among them are decimal-exact. The tool does not include CGS units (statvolt = 299.7925 V) or specialized units like microvolts-RMS vs peak; if your data sheet specifies RMS or peak-to-peak, you must apply that scaling separately before entering values here.

How small is a microvolt and how large is a megavolt in practice?

1 microvolt is 10^-6 V, the noise floor of a quiet electrocardiogram or the signal level at a sensitive radio antenna input. 1 millivolt (10^-3 V) is the typical EEG brain-wave amplitude or thermocouple output per degree. 1 V is the EMF of a single zinc-carbon cell. 1 kilovolt (10^3 V) appears in cathode-ray tubes, X-ray tubes (30 to 150 kV), and high-voltage DC transmission. 1 megavolt (10^6 V) is reached by Van de Graaff generators, lightning strikes (50 to 100 MV), and ultra-high-voltage power lines (1 MV UHV-DC links in China). So the converter spans the full 10^12 dynamic range from neuron signals to thunderstorms.

When should I use mV vs V vs kV?

Pick the prefix that keeps the numeric value between roughly 0.1 and 999 for readability. Use uV for instrumentation amplifier inputs, thermocouple signals, biopotential measurements, and RF receiver inputs. Use mV for sensor outputs (most Hall-effect, strain-gauge, pH electrodes give millivolts), low-power analog signals, and battery cell voltages quoted in mV-per-cell. Use V for everything in consumer electronics, automotive (12 V), batteries (1.5 V, 3.7 V, 9 V). Use kV for X-ray, automotive ignition (10 to 40 kV at the spark plug), distribution transformers (11, 22, 33 kV), and CRT anode supplies. Use MV only for ultra-high-voltage transmission and accelerator physics.

How precise are the conversions and what about uncertainty?

Prefix conversions use exact powers of ten and 64-bit floating-point internally, so they are accurate to 15+ decimal digits. However, real-world voltage measurements rarely justify more than 4 to 6 significant figures. Multimeter accuracy is typically +/-(0.5% reading + 2 digits) for handhelds and +/-(0.005% + 1 digit) for 6.5-digit bench meters. Calibrators traceable to the Josephson voltage standard reach parts per billion. Display only as many digits as your input justifies: converting a 3.7 V battery reading to 3,700.000 mV implies false precision. The Josephson standard, based on the AC Josephson effect (V = n*h*f / 2e), is the SI primary realization of the volt since 1990 (revised 2019).

What is the difference between DC, AC RMS, and peak voltage?

These are three different measures and the converter treats your input as a pure number; you must know which you have. DC voltage is the constant-amplitude level read by any meter in DC mode. AC RMS (root-mean-square) is the DC-equivalent heating voltage: 120 V AC mains is 120 V RMS, but the peak is 120 * sqrt(2) = 169.7 V and peak-to-peak is 339.4 V. The crest factor for a pure sinusoid is sqrt(2) = 1.4142. For other waveforms (square, triangular, distorted mains) the crest factor differs and you need a true-RMS meter to read RMS correctly. Always state whether a voltage is DC, RMS, peak, or peak-to-peak in technical documentation.

Why does my battery read 9.6 V when its label says 9 V?

Labelled battery voltage is the nominal mid-discharge value, not the open-circuit terminal voltage. A fresh 9V alkaline reads about 9.4 to 9.6 V open-circuit, drops to 9.0 V under load mid-life, and reaches end-of-life around 6 to 7 V. Similarly, a 12 V lead-acid car battery sits at 12.6 to 12.8 V fully charged (resting), 13.8 to 14.4 V while charging, and 11.8 V near discharged. Lithium-ion cells nominally 3.7 V swing from 4.2 V full to 3.0 V empty. Treat nameplate voltages as a class label, not a precision specification. The converter performs pure mathematics; it does not know whether your number is loaded, unloaded, charging, or RMS.

How is the volt defined in the modern SI system?

Since the 2019 SI redefinition, the volt is defined by fixing the elementary charge e at exactly 1.602176634 x 10^-19 C, the Planck constant h at exactly 6.62607015 x 10^-34 J*s, and the second via the caesium frequency. The volt is then realized via the Josephson constant K_J = 2e/h = 483597.8484... GHz/V (exact). At an irradiated Josephson junction, voltage steps appear at V = n*f/K_J with parts-per-billion accuracy. Before 2019, the volt was conventionally tied to K_J-90 = 483597.9 GHz/V (exact by convention since 1990). The 2019 revision retired this convention because the SI now fixes the underlying constants instead. The BIPM and national metrology institutes (NIST, NPL, PTB) maintain Josephson array voltage standards.

What are edge cases to watch out for in voltage conversion?

First, signed voltages: a -5 V supply is mathematically negative, and the converter preserves sign through prefix changes. Second, common-mode vs differential voltage: a 1 kV common-mode signal can ride on a 10 mV differential, and meters measure whichever input pair you probe. Third, voltage vs potential: 'voltage' is always a difference; 'potential' implies a reference (often earth ground). Fourth, instantaneous vs average for non-sinusoidal waveforms: the math for a half-wave-rectified sine, a square wave, or a triangular wave each has a different RMS-to-peak ratio. Fifth, very high voltages (>10 kV) involve corona, ionization, and breakdown not captured by simple arithmetic. The converter handles the units; the physics is on you.

Units

Volt (V)

The SI unit of electric potential difference. One Volt is the potential difference that will drive one Ampere of current through a resistance of one Ohm. Common household voltages are 120V (North America) or 230V (Europe). USB devices operate at 5V.

Millivolt (mV)

One thousandth of a Volt (0.001 V). Used in sensors, thermocouples, and biomedical applications. ECG signals are typically measured in millivolts. Battery cells often show voltage differences in millivolts during testing.

Microvolt (µV)

One millionth of a Volt (0.000001 V). Essential in medical instrumentation for measuring brain waves (EEG), sensitive scientific instruments, and low-noise amplifier specifications. Human brain signals are in the microvolt range.

Kilovolt (kV)

One thousand Volts. Used in power distribution, X-ray machines, and industrial applications. Residential power lines typically carry 4-35 kV, while high-voltage transmission lines operate at 110-765 kV.

Megavolt (MV)

One million Volts. Found in ultra-high voltage power transmission, particle accelerators, and lightning research. Lightning strikes can produce voltages exceeding 100 MV. Some power transmission systems operate at 1 MV or higher.

Common Voltage Conversions