Precision Utility
Ohm's Law
Calculator
Core Law
V = I × R
Variables
4
Enter any two electrical values — voltage, current, resistance or power — and the calculator instantly solves the other two using Ohm's law and the power equation. Ideal for students, engineers and hobbyists working with DC circuits.
Enter Any Two Values
Fill in exactly two fields. The calculator solves the rest.
Solved Equation
Enter two values to begin
Voltage
—
volts (V)
Current
—
amps (A)
Resistance
—
ohms (Ω)
Power
—
watts (W)
How the Ohm's law calculator works
Enter any two of the four electrical quantities — voltage (V), current (I), resistance (R) or power (P). The calculator detects which two fields you have filled in and solves the remaining two instantly.
It uses Ohm's law (V = I × R) as the foundation, combined with the electrical power equation (P = V × I). From these two relationships, every combination of two knowns can be solved:
- V and I known: R = V / I, P = V × I
- V and R known: I = V / R, P = V² / R
- V and P known: I = P / V, R = V² / P
- I and R known: V = I × R, P = I² × R
- I and P known: V = P / I, R = P / I²
- R and P known: V = √(P × R), I = √(P / R)
Results appear in the result card on the right. Panels are highlighted to show which values were given and which were calculated.
What you need to know about Ohm's law and circuits
Ohm's law is one of the most fundamental principles in electrical engineering and physics. Discovered by Georg Simon Ohm in 1827, it describes the linear relationship between voltage, current and resistance in a conductor.
Key points to understand:
- Voltage (V) is the electrical pressure or potential difference measured in volts. It drives current through a circuit.
- Current (I) is the flow rate of electric charge measured in amperes. Higher voltage or lower resistance means more current.
- Resistance (R) is the opposition to current flow measured in ohms (Ω). Every material has some resistance.
- Power (P) is the rate of energy transfer measured in watts. A 60 W bulb converts 60 joules of electrical energy per second.
Ohm's law applies directly to DC (direct current) circuits and to purely resistive AC circuits. For AC circuits with capacitors or inductors, impedance replaces simple resistance.
In practice, Ohm's law is used daily by electricians sizing cables, engineers designing circuit boards and students learning electronics. It is the starting point for almost every electrical calculation.
Frequently asked questions
What is Ohm's law?
Ohm's law states that the current flowing through a conductor is directly proportional to the voltage across it and inversely proportional to its resistance. The formula is V = I × R, where V is voltage in volts, I is current in amps and R is resistance in ohms.
How do I use this Ohm's law calculator?
Enter any two of the four values — voltage (V), current (I), resistance (R) or power (P). The calculator automatically solves the other two using Ohm's law and the power equation. Clear a field to change which values you are entering.
What is the relationship between power, voltage and current?
Electrical power (measured in watts) equals voltage multiplied by current: P = V × I. This can also be expressed as P = I² × R or P = V² / R by substituting Ohm's law.
What units does Ohm's law use?
Ohm's law uses SI units: voltage in volts (V), current in amperes (A), resistance in ohms (Ω) and power in watts (W). The calculator accepts and displays values in these standard units.
Can I calculate resistance from power and current?
Yes. If you know power (P) and current (I), resistance is R = P / I². Enter the power and current values into the calculator and it will compute resistance and voltage for you automatically.
Does Ohm's law apply to AC circuits?
Ohm's law applies directly to DC circuits. In AC circuits, the concept extends to impedance (Z) instead of pure resistance. This calculator is designed for simple DC circuits using pure resistance values.