Ohms Law CalculatorFree online other calculator — instant results, no sign-up
Voltage, current, resistance and power from any two.
About the Ohms Law Calculator
This calculator determines the missing electrical parameter among voltage, current, and resistance using Ohm's law, while also calculating the resulting electrical power. It is designed for students, electronics hobbyists, and technicians working with DC circuits or simple resistive AC circuits.
- Voltage (V, 0 if unknown)
- Electrical potential difference in volts (V). Enter 0 if this is the value you need to solve for.
- Current (A)
- Electric current flow in amperes (A). Enter 0 if this is the value you need to solve for.
- Resistance (Ω)
- Opposition to electrical current in ohms (Ω). Enter 0 if this is the value you need to solve for.
Formula and method
If V = 0: V = I × R If I = 0: I = V / R If R = 0: R = V / I P = V × I
- VVoltage across the component in volts (V)
- ICurrent flowing through the component in amperes (A)
- RResistance of the component in ohms (Ω)
- PElectric power dissipated in watts (W)
The tool checks which of the three primary inputs is set to zero or omitted, evaluating V = I × R first, then I = V / R, and lastly R = V / I. Once all three quantities are established, electrical power is calculated as P = V × I. All results are formatted to four decimal places.
Worked example
These are the calculator's starting values and the results it actually produces for them.
Inputs
- Voltage (V, 0 if unknown)12
- Current (A)0.5
- Resistance (Ω)0
Results
- Voltage12 V
- Current0.5 A
- Resistance24 Ω
- Power6 W
How to use the Ohms Law Calculator
- 1Enter two known values among voltage (V), current (A), and resistance (Ω).
- 2Set the unknown variable to 0.
- 3The calculator applies the corresponding Ohm's law transformation to solve for the missing parameter.
- 4Read the resolved voltage, current, resistance, and the total dissipated power in watts.
Reading your result
The output displays all four core electrical values: voltage (V), current (A), resistance (Ω), and power (W). The power metric shows the rate of energy dissipation or consumption by the resistive load. A higher current or voltage for a given resistance will sharply increase the power.
Limitations
The calculator assumes an ideal, linear, pure-resistive DC circuit. It does not account for temperature coefficients, component tolerances, reactive impedance (capacitance or inductance), or AC phase angles.
Common questions
What happens if all three inputs are provided?+
Can I use this calculator for AC circuits?+
Why is power calculated as V × I?+
Does the calculator save my information?+
Calculations run in your browser. While signed in, inputs and results are automatically recorded in account history; saving a result creates a separate saved record.
Further reading
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Results are estimates for informational purposes and are not financial, medical or legal advice.