Solve any circuit from two knowns.
Enter any two of voltage, current, resistance and power. See the other two solved instantly, the full power triangle, and every core equation with your numbers plugged in.
Your circuit
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Core equations with your values
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How Ohm's Law works
Understanding Ohm's Law
Ohm's Law states that V = I x R, where V is voltage in volts, I is current in amperes, and R is resistance in ohms. This fundamental relationship governs all electrical circuits and is essential for electrical design and troubleshooting.
The Power Equation
Power (P) in watts equals voltage times current: P = V x I. Combined with Ohm's Law, this gives P = I²R and P = V²/R. These formulas let you calculate power from any two of the three basic electrical quantities.
Practical Applications
Use Ohm's Law to size resistors in circuits, calculate current draw for fuse selection, determine wire gauge requirements, and troubleshoot electrical problems. It applies to DC circuits directly and to AC circuits with adjustments for impedance.
Series vs Parallel Circuits
In series circuits, current is the same through all components and voltages add up. In parallel circuits, voltage is the same across all branches and currents add up. Ohm's Law applies to each component individually and to the circuit as a whole.
Common questions
How do I use this calculator?
Enter any two known values (voltage, current, resistance) and leave the third at 0. The calculator will compute the missing value and also calculate the power in watts. For example, enter 12V and 2A to find 6 ohms resistance and 24 watts.
What is the relationship between voltage, current, and resistance?
Voltage is the electrical pressure, current is the flow of electrons, and resistance opposes that flow. Higher voltage or lower resistance increases current. V = I x R, I = V / R, and R = V / I are the three forms of Ohm's Law.
Does Ohm's Law apply to AC circuits?
Ohm's Law applies to AC circuits when you replace resistance with impedance (Z), which includes resistance plus reactance from capacitors and inductors. For purely resistive AC loads (like heaters), Ohm's Law works directly.
What is a watt?
A watt is the unit of electrical power equal to one volt times one ampere. A 60-watt light bulb at 120 volts draws 0.5 amps. Watts measure the rate of energy consumption or production.
Estimates only. Ohm's Law applies directly to DC and purely resistive loads; AC circuits with reactance require impedance.