Joules to Volts Calculator

Q: How many volts is 300 joules?

It depends on the charge. At 1 coulomb, 300 joules = 300 volts. At 5 coulombs, 300 joules = 60 volts. Use the calculator with your actual charge value.

Q: What is 200 joules in volts?

200 joules at 1 coulomb is 200 V. At 2 coulombs it is 100 V. At 10 coulombs it is 20 V.

Q: Can I convert joules to volts without knowing the charge?

No. You need either the charge (coulombs) or the capacitance (farads) to make the conversion.

Q: How do I convert 500 joules to volts?

Use V = E ÷ Q. For 500 J and 10 C, V = 50 V. For a capacitor, use V = √(2 × 500 ÷ C).

Q: What is the formula for joules to volts in a capacitor?

V = √(2E / C), where E is energy in joules and C is capacitance in farads.

Converting energy (joules) to voltage (volts) isn't a direct one-step calculation. You need one more piece of information: either the charge (in coulombs) or the capacitance (in farads). This tool handles both cases. Enter your values below to get the voltage instantly.

Calculator

What do you know? Energy (joules)

Charge (coulombs)

The formulas

1. Using charge

If you know the energy in joules (E) and the charge in coulombs (Q), voltage is:

V (volts) = E (joules) ÷ Q (coulombs)

Example: 300 joules ÷ 5 coulombs = 60 volts.

2. Using capacitance

For a capacitor, the stored energy is E = ½ × C × V². Rearranging to solve for voltage:

V (volts) = √(2 × E (joules) ÷ C (farads))

Example: 300 joules with a 0.1 F capacitor: √(2 × 300 ÷ 0.1) = √6000 ≈ 77.46 volts.

Why the two formulas? Joules measure energy. Volts measure energy per unit of charge. If you only have energy, you must know either how much charge is involved (the first formula) or the capacitance of the component storing it (the second). There is no way around this — a joule alone does not determine a voltage.

Common conversions (quick reference)

The table below assumes a charge of 1 coulomb for simplicity. Real circuits will have different charge values, but this shows the pattern.

Energy (J)	Voltage (V) at 1 C	Voltage (V) at 5 C
100 J	100 V	20 V
200 J	200 V	40 V
300 J	300 V	60 V
400 J	400 V	80 V
500 J	500 V	100 V
1000 J	1000 V	200 V

Remember: these numbers are only valid for the charge listed. For a different charge, divide the joule value by that charge to get volts.

Frequently asked questions

How many volts is 300 joules?

It depends on the charge. At 1 coulomb, 300 joules = 300 volts. At 5 coulombs, 300 joules = 60 volts. Use the calculator above with your actual charge value to get the exact answer.

What is 200 joules in volts?

Again, the charge matters. 200 joules at 1 C is 200 V. At 2 C it is 100 V. At 10 C it is 20 V. If you know the capacitance instead, use the second formula: V = √(2E/C).

Can I convert joules to volts without knowing the charge?

No. Joules and volts measure different things. You need either the charge (coulombs) or the capacitance (farads) to make the conversion. Any tool that claims to convert joules to volts directly is either assuming a charge value or using a capacitor formula without telling you.

How do I convert 500 joules to volts?

Use V = E ÷ Q. For 500 J and 10 C, V = 50 V. For 500 J and 2 C, V = 250 V. If you have a capacitor, use V = √(2 × 500 ÷ C). For example, with C = 0.01 F, V ≈ 316.2 V.

What is the formula for joules to volts in a capacitor?

The energy stored in a capacitor is E = ½ C V². Solving for V gives V = √(2E / C). This is the formula to use when you know the capacitance in farads.

Is 1 joule equal to 1 volt?

No. They are different units. One joule is one coulomb multiplied by one volt (J = C × V). So 1 joule with 1 coulomb of charge corresponds to 1 volt, but the joule itself is an energy unit, not a voltage unit.

What about joules to electron volts (eV)?

That is a different conversion. 1 electron volt = 1.602 × 10⁻¹⁹ joules. To convert joules to eV, divide by 1.602 × 10⁻¹⁹. This calculator is specifically for joules to volts, not eV.