Solve any electrical unknown. This free Ohm’s law calculator takes any two of voltage, current, resistance or power and computes the other two using V = I × R and P = V × I.
Enter any two
volts
amps
ohms (Ω)
watts
Fill in any two values and the calculator works out the rest using Ohm’s law (V = I × R) and the power law (P = V × I). Enter exactly two to solve.
Results
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Enter any two values
Voltage
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Current
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Resistance
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Power
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Ohm’s law: V = I × R. Power: P = V × I (also P = I²R = V²/R). Voltage in volts, current in amps, resistance in ohms (Ω), power in watts.
Use this free Ohm’s law calculator to find voltage, current, resistance or power. Enter any two values and it works out the rest using V = I × R and P = V × I.
What this Ohm’s law calculator does
An Ohm’s law calculator relates voltage (V), current (I), resistance (R) and power (P). Give it any two and it solves for the other two instantly.
The formulas
V = I × R (Ohm's law)
P = V × I = I²R = V²/R (electrical power)
So 2 amps through 10 ohms gives 20 volts and 40 watts; 12 volts across 4 ohms gives 3 amps and 36 watts.
The four quantities
Quantity
Symbol
Unit
Voltage
V
volts (V)
Current
I
amps (A)
Resistance
R
ohms (Ω)
Power
P
watts (W)
How Ohm’s law works
Ohm’s law says current is proportional to voltage and inversely proportional to resistance. Raise the voltage and more current flows; raise the resistance and less flows. Power is the rate of energy use — voltage times current.
How to use the Ohm’s law calculator
Enter any two of voltage, current, resistance or power.
Leave the others blank.
Read all four values instantly.
Ohm's Law FAQ
What is Ohm's law?
Ohm's law states that voltage equals current times resistance: V = I × R. Rearranged, I = V/R and R = V/I.
How do I calculate power?
Power is voltage times current: P = V × I. It can also be written P = I²R or P = V²/R.
How many values do I need?
Just two. From any two of voltage, current, resistance or power, the calculator finds the other two.
How do I find resistance from voltage and current?
Divide voltage by current: R = V ÷ I. For example, 12 V and 3 A gives 4 Ω.
Does it work for AC circuits?
It covers ideal DC circuits. AC circuits use impedance instead of plain resistance, so results are an approximation there.
Is the Ohm's law calculator free?
Yes, this Ohm's law calculator is completely free, needs no sign-up, and gives instant results in your browser.
