Ohm's law calculator
Solve voltage, current, resistance, and power from any valid pair of known values.
What this calculator covers
Use this calculator when you know any two steady-state electrical values and want the other two without rearranging the formulas by hand.
The walkthrough keeps the core V = I x R and P relationships visible so it is easier to audit how the missing values were solved.
Frequently asked questions
- What two values do I need to use this calculator?
- You need any two distinct electrical quantities from voltage (V), current (A), resistance (ohms), and power (W). The calculator accepts all six valid pairs and derives the remaining two from the appropriate equation.
- Does Ohm's law apply to AC circuits?
- The relationships V = IR and P = VI hold for DC circuits and for AC circuits when using RMS-equivalent values and resistive (non-reactive) loads. For circuits with capacitance or inductance, impedance replaces simple resistance and additional phase considerations apply.
- Why can't I enter zero for current or resistance?
- Dividing by zero produces an undefined result. Zero current means no power can flow through the circuit, making resistance and power indeterminate. Zero resistance in a real circuit would imply a short, which the idealized equations cannot model.
- Is this calculator suitable for electrical engineering design work?
- This calculator covers idealized steady-state relationships and is intended for educational and quick-check use. Professional electrical design must follow applicable codes and standards, and should not rely solely on simplified formula results.
Tool
Run the calculation
Result
RESULT · SOLVED VALUES
â„–190
Primary result
12 ohms · 1,200 W
Starting with Voltage = 120 V and Current = 10 A, Ohm's law resolves the remaining values as 12 ohms and 1,200 W.
- Voltage
- 120 V
- Current
- 10 A
- Resistance
- 12 ohms
- Power
- 1,200 W
Step-by-step solution
- 1.Validate that the two known inputs are different electrical quantities and that neither value is negative.
- 2.Choose the matching Ohm's law relationship for the known pair to solve the missing current, voltage, resistance, or power values.
- 3.Cross-check the solved values against V = I x R and P = V x I so both missing outputs stay internally consistent.
Walkthrough
Visual walkthrough
Ohm's law links voltage, current, resistance, and power. Once any valid pair is known, the other two can be derived algebraically.
01
Start from two known quantities
Voltage = 120 V; Current = 10 A
The calculator accepts any two distinct values from voltage, current, resistance, and power.
02
Apply the matching equations
V = I x R; P = V x I; P = I^2 x R; P = V^2 / R
Each input pair maps to the equation that solves the remaining values without guessing.
03
Read the solved pair
The result panel surfaces the two derived quantities together so you can verify the full electrical relationship.
12 ohms · 1,200 W