Joules to Volts Calculator

Convert energy and charge into voltage, or solve for any one value.

Supports joules, coulombs, and volts across eV, Wh, kWh, pC, nC, mV, kV and more.

Updated August 21, 2026

CreatorFrank Zhao

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Overview

This Joules to Volts Calculator converts between $E$ (energy), $Q$ (electric charge), and $V$ (voltage) using the single physics relation $V = E / Q$ . Enter any two values and the calculator solves for the third — in either direction — with full multi-unit support.

Core relation

V = \frac{E}{Q}\quad\Longleftrightarrow\quad E = V \cdot Q \quad\Longleftrightarrow\quad Q = \frac{E}{V}

$V$ in volts, $E$ in joules, $Q$ in coulombs

It is useful for students checking homework, hobbyists sizing batteries or capacitors, and engineers doing quick energy-per-charge estimates. Unlike a one-way converter, the intelligent bidirectional engine keeps all three fields in sync: change voltage and the charge or energy updates automatically.

How to use

Pick your two known values

For example, you know the energy stored and the charge that carries it, and you want the voltage.

Enter the numbers and choose units

Energy offers J, kJ, MJ, Wh, kWh, eV, keV, MeV. Charge offers pC, nC, μC, mC, C and elementary charges (e). Voltage offers nV, μV, mV, V, kV, MV. The calculator converts to base SI (J, C, V) automatically.

Read the third value

The remaining field fills in and is highlighted. Leave the field you want solved empty — for instance, leave Volts blank to get $V = E/Q$ .

Worked example — the fixture the calculator uses internally

Energy $E = 1000\ \mathrm{J}$ , charge $Q = 10\ \mathrm{C}$ → voltage?

V

=

\frac{E}{Q}

=

\frac{1000}{10}

=

100\ \mathrm{V}

Try other directions with the same numbers: $Q = E/V = 1000/100 = 10\ \mathrm{C}$ and $E = Q\cdot V = 10\times 100 = 1000\ \mathrm{J}$ . Clearing a field or editing any value triggers an automatic recalculation. If you set charge to $0$ with non-zero energy, voltage shows $\infty$ (Infinity) — the only place the calculator uses infinity — while $0/0$ stays blank as undefined.

Formula explained

Voltage is defined as energy per unit charge. For a charge $Q$ moved through a potential difference $V$ , the work done is $E = V\cdot Q$ . Rearranging gives the two inverse forms the calculator also supports.

V = \frac{E}{Q},\qquad Q = \frac{E}{V},\qquad E = V\cdot Q

Variables

$V$ — voltage (volts, V). The third field uses infinity display: $V=\infty$ only when $E\neq 0,\ Q=0$ .
$E$ — energy (joules, J). Display units scale by fixed SI factors: $1\ \mathrm{kJ}=10^{3}\mathrm{J}$ , $1\ \mathrm{Wh}=3600\ \mathrm{J}$ , $1\ \mathrm{kWh}=3.6\times10^{6}\mathrm{J}$ .
$Q$ — electric charge (coulombs, C). Sub-units scale by powers of ten: $1\ \mathrm{mC}=10^{-3}\mathrm{C}$ , $1\ \mathrm{\mu C}=10^{-6}\mathrm{C}$ , etc.
Elementary charge: $1\ e = 1.602176634\times10^{-19}\ \mathrm{C}$ exactly by the 2019 SI redefinition (the same constant links $1\ \mathrm{eV}=1.602176634\times10^{-19}\ \mathrm{J}$ ).

How units are handled

Each dropdown only changes the display factor $f$ . Internally the calculator stores base SI values: $E_{\mathrm{J}} = E_{\mathrm{display}}\cdot f_E$ , $Q_{\mathrm{C}} = Q_{\mathrm{display}}\cdot f_Q$ , $V_{\mathrm{V}} = V_{\mathrm{display}}\cdot f_V$ and solves $V_{\mathrm{V}} = E_{\mathrm{J}}/Q_{\mathrm{C}}$ before converting back: $V_{\mathrm{display}} = V_{\mathrm{V}}/f_V$ . So $3600\ \mathrm{J}$ viewed as $1\ \mathrm{Wh}$ or $0.001\ \mathrm{kWh}$ does not change the underlying result.

Assumptions: the relation is evaluated for an ideal lumped charge at a single potential difference, ignoring time dependence, losses, and internal resistance. For AC, pulsed, or capacitor energy ( $E=\tfrac12 CV^2$ ), use a dedicated power or capacitance tool instead.

Real-world examples

Example 1 — Small battery

A 5 Wh lithium cell (≈ $18000\ \mathrm{J}$ ) delivers $4500\ \mathrm{C}$ (≈ 1.25 Ah) during a test discharge. What was its average voltage?

V

=

E/Q

=

18000/4500

=

4.0\ \mathrm{V}

Enter $E=5\ \mathrm{Wh}$ (switch energy to Wh) and $Q=4500\ \mathrm{C}$ — voltage fills as $4\ \mathrm{V}$ , a typical single-cell Li-ion under load. If you switch voltage to mV you will read $4000\ \mathrm{mV}$ .

Example 2 — Elementary charges

An electron beam deposits $1\ \mathrm{MeV}=10^{6}\ \mathrm{eV}$ of energy via $10^{12}$ elementary charges. Express the accelerating voltage in kV.

E = 10^{6}\times 1.602\times10^{-19}

=

1.60\times10^{-13}\ \mathrm{J}

Q = 10^{12}\times1.602\times10^{-19}

=

1.60\times10^{-7}\ \mathrm{C}

V = E/Q \approx 10^{-6}\ \mathrm{V}\times\frac{f_{\mathrm{MeV}}}{f_{e}}

=

1000\ \mathrm{V}=1\ \mathrm{kV}

In practice just enter $E=1\ \mathrm{MeV}$ and $Q=10^{12}\ e$ (select e for charge) — the calculator handles the $1.602\times10^{-19}$ factor and returns $1\ \mathrm{kV}$ . Switch energy to $keV$ or voltage to $MV$ to cross-check.

Next step: if you need energy from power and time, try our Power Converter or estimate stored charge with the Capacitance Converter.

Tips & best practices

Match pC / nC / μC carefully

A factor of 1000 error is the most common mistake. pC is $10^{-12}\mathrm{C}$ , nC is $10^{-9}\mathrm{C}$ , μC is $10^{-6}\mathrm{C}$ . Double-check the dropdown after pasting a datasheet value.

Do not confuse charge with capacity

Ampere-hours (Ah) and coulombs both describe charge, but this calculator expects coulombs or e. Convert Ah to C first ( $1\ \mathrm{Ah}=3600\ \mathrm{C}$ ) before entering.

Keep the solved field empty

If all three fields have values, the engine preserves the two you edited most recently. To force a fresh solve, clear the field you want computed.

Use eV ↔ J via the energy dropdown

Select eV, keV, or MeV for energy to let the calculator apply the exact $1.602176634\times10^{-19}$ factor; do not pre-convert by hand and risk rounding.

Frequently asked questions

Can the result be negative?

Yes, mathematically. The calculator accepts negative energy or charge and will return a signed voltage. Physically that just means the charge sign or energy flow direction is reversed.

Why does voltage show Infinity?

Only when you enter a non-zero energy with charge $Q=0$ . By design $V=E/Q$ is evaluated as signed infinity there. If both are zero ( $0/0$ ) the result stays blank as undefined.

Do I need to convert Wh or Ah myself?

No. For energy pick Wh or kWh directly. For charge measured in Ah, convert to coulombs ( $1\ \mathrm{Ah}=3600\ \mathrm{C}$ ) before entering, or consider using our Energy Conversion helper to prepare the value.

Limitations

•This is a pure $V=E/Q$ calculation. It does not model losses, internal resistance, efficiency, or time-varying waveforms. For capacitors, batteries, or AC systems use a dedicated model.
•Values are computed with high internal precision and then formatted for display. Very large or very small inputs may show scientific notation — the underlying value remains exact.
•The calculator does not validate physical plausibility (for example, an unphysically large charge for a small component). Always sanity-check results against your device datasheet.

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