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Ohm's Law Calculator

Solve any two-variable electrical circuit problem using Ohm's Law (V = IR) and Watt's Law (P = VI). Select which quantity you want to find, enter any two known values, and instantly see all four quantities: Voltage, Current, Resistance, and Power.

Select what you want to find:

Ohm's Law & Watt's Law Formulas

V = I × R Voltage = Current × Resistance
I = V / R Current = Voltage ÷ Resistance
R = V / I Resistance = Voltage ÷ Current
P = V × I Power = Voltage × Current
P = I² × R Power = Current² × Resistance
P = V² / R Power = Voltage² ÷ Resistance

How to Use the Ohm's Law Calculator

  1. 1
    Choose What to Find
    Select the quantity you want to solve for: Voltage (V), Current (I), Resistance (R), or Power (P).
  2. 2
    Enter Two Known Values
    Input any two known electrical values. The calculator accepts any valid pair that uniquely determines the circuit.
  3. 3
    Click Calculate
    All four quantities — Voltage, Current, Resistance, and Power — are calculated and displayed simultaneously.
  4. 4
    Review All Results
    Results are shown in a 2×2 grid. Copy them with one click for use in reports or documentation.

Example Calculation

A 12V battery drives a current of 2A through a resistor:

Voltage (V) = 12 V | Current (I) = 2 A
Resistance R = V / I = 12 / 2 = 6 Ω
Power P = V × I = 12 × 2 = 24 W
'Why can\'t I just enter one value?', 'answer' => 'Two independent values are always required to uniquely determine a circuit. One value alone is insufficient: knowing only 12V tells you nothing about current or resistance without an additional constraint.'], ['question' => 'What units does this calculator use?', 'answer' => 'Voltage is in Volts (V), current in Amperes (A), resistance in Ohms (Ω), and power in Watts (W). Enter values in these base units; the calculator handles all conversions internally.'], ]" />

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