Volts to Joules Calculator

Q: How many joules is 1 volt?

1 volt moves 1 joule of energy per coulomb of charge. Without knowing the charge, a voltage can't be converted to joules.

Q: How do I convert volts to joules with amp-hours?

Convert amp-hours to coulombs (× 3,600), then multiply by voltage. 2 Ah at 12 V: 2 × 3,600 × 12 = 86,400 J.

Q: What is an electronvolt?

An electronvolt (eV) is the energy one electron gains moving through 1 volt: 1.602177e-19 joules. It is the standard energy unit in atomic and particle physics.

Q: Why is capacitor energy ½QV and not QV?

Because the capacitor's voltage starts at zero and rises to V as it charges, so the average voltage the charge moves through is V/2. A battery keeps a roughly constant voltage, so E = QV applies.

Convert volts to joules using electric charge: E = V × Q. Calculate the energy transferred when a charge in coulombs moves through a voltage.

🔌 VOLTAGE

⚡ CHARGE

ENERGY

120 J

IN kJ

0.12 kJ

FORMULA

J = V × C

IN Wh

0.033 Wh

💡 How to Convert Volts to Joules

To convert volts to joules, multiply the voltage by the charge in coulombs. A volt is defined as one joule per coulomb, so energy (J) = voltage (V) × charge (C). Volts alone can't be converted to joules: you always need the amount of charge that moves.

Volts to joules formula

E = V × Q

E = energy in joules, V = voltage in volts, Q = charge in coulombs
Example: 12 V × 10 C = 120 J

Worked examples

Car battery delivering 100 Ah: 100 Ah = 100 × 3,600 = 360,000 C. At 12 V, 12 × 360,000 = 4,320,000 J (4.32 MJ, or 1.2 kWh).
AA alkaline cell: roughly 2.5 Ah = 9,000 C at a nominal 1.5 V gives about 13,500 J. Real output is lower because the voltage falls as the cell discharges.
Single electron through 1 V: 1.6022e-19 C × 1 V = 1.6022e-19 J, the definition of one electronvolt (eV).

Volts to joules table

Voltage (V)	Charge (C)	Energy (J)
1.5	1	1.5
1.5	9,000	13,500
3.7	18,000	66,600
5	10	50
9	100	900
12	10	120
12	360,000	4,320,000
120	1	120
230	2	460
1,000	0.5	500

The units behind the formula

Joule (J): the SI unit of energy. 1 J = 1 watt for 1 second = 1 volt × 1 coulomb.
Volt (V): electric potential difference, defined as 1 joule of energy per coulomb of charge.
Coulomb (C): electric charge. One coulomb is the charge carried by a current of 1 ampere in 1 second, about 6.242 × 10¹⁸ electrons.
Watt (W): power, the rate of energy transfer. 1 W = 1 J per second.

Converting amp-hours to coulombs

Battery capacity is usually given in amp-hours or milliamp-hours. Convert to coulombs with 1 Ah = 3,600 C and 1 mAh = 3.6 C, then multiply by voltage. The result in joules divided by 3,600 gives watt-hours.

Capacitors are different

E = V × Q assumes the charge moves through a constant voltage, as with a battery. A capacitor charged from 0 V up to V stores only E = ½ × Q × V (or ½ × C × V²), because the voltage rises as charge builds up. Use the capacitance to charge calculator for capacitor problems.

Related conversions: joules to volts · watts to joules · joules to watts

Joules = volts × coulombs. 12 V × 10 C = 120 J. You need the charge; voltage alone can't be converted.