What formulas does this calculator use?

When current is given: E (J) = I² × R × t. When voltage is given: E (J) = V² / R × t. Both are derived from Ohm's Law (V = IR) and the power equation P = I²R = V²/R, combined with E = P × t.

What is Joule heating?

Joule heating (also called resistive or ohmic heating) is the process by which electrical energy is converted to heat when current flows through a resistance. The energy released is given by E = I² × R × t and is always positive regardless of current direction.

When should I use the voltage mode instead of the current mode?

Use voltage mode when you know the voltage across the resistor but not the current. This is common in parallel circuits where voltage is fixed. Use current mode when you know the current through the resistor, as in series circuits.

Why does energy scale with I squared?

Power in a resistor is P = I² × R. Doubling the current quadruples the power — and therefore the energy dissipated for the same duration. This quadratic relationship is why high-current connections require careful thermal management.

Can I use this for AC circuits?

Yes, if you enter RMS values for current or voltage. The formulas E = I²Rt and E = V²t/R give the correct real energy for purely resistive AC loads when RMS quantities are used.

What is the difference between joules and watts?

Watts measure power (energy per second), while joules measure total energy. The relationship is E (J) = P (W) × t (s). A 10 W resistor operating for 5 seconds dissipates 50 J of heat.

Ohms to Joules Calculator

Calculate energy in joules from resistance (ohms), current or voltage, and time using E = I²Rt or E = V²t/R.

Input Parameters

Calculation Mode

Resistance (Ω)

Current (A)

Time (s)

Result

Enter values and press Calculate

Formula Reference

Using Current

E (J) = I² × R (Ω) × t (s)

Joule's First Law of Heating

Using Voltage

E (J) = V² / R (Ω) × t (s)

Derived via Ohm's Law (V = IR)

Power (Current)

P (W) = I² × R (Ω)

Power (Voltage)

P (W) = V² / R (Ω)

Result copied!

Summary

This calculator converts resistance in ohms along with current or voltage and time into energy in joules. When current is known, it applies E = I² × R × t (Joule heating formula). When voltage is known, it uses E = V² / R × t. Both formulas derive from Ohm's Law (V = IR) and the definition of electrical power (P = I²R = V²/R). The tool is useful for estimating heat dissipation in resistors, wires, and heating elements.

How it works

Select the calculation mode: use current (I) or use voltage (V).
Enter the resistance in ohms (Ω).
Enter the current in amperes or the voltage in volts, depending on the selected mode.
Enter the time duration in seconds.
Press Calculate — the tool applies E = I²Rt or E = V²t/R and displays energy in joules.
Additional unit conversions (kJ, Wh, kWh) are shown automatically.

Use cases

Calculate heat dissipated in a resistor during circuit operation.
Estimate energy lost in a wire due to its resistance over time.
Size fuses and thermal protection based on expected joule heating.
Determine energy delivered by a heating element at a given voltage.
Verify power budgets in PCB design by checking resistive losses.
Calculate energy stored and released in resistive discharge circuits.
Estimate derating requirements for resistors under continuous load.
Educational use to explore Joule's First Law of Heating.

Frequently Asked Questions

Last updated: 2026-05-23 · Reviewed by Nham Vu