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Ohm's Law Calculator

Calculate voltage, current, resistance, and electrical power with interactive Ohm's Law formulas.

1. Enter your numbers  →  2. Check the answer  →  3. Read the steps before you trust it

V
A
W

Ohm's Law Calculated Values

Voltage (V)
12V
Current (I)
2A
Resistance (R)
6Ω
Power (P)
24W

Step-by-Step Engineering Calculation

  1. 1Resistance: R=VI=12 V2 A=6.0000 ΩR = \frac{V}{I} = \frac{12\text{ V}}{2\text{ A}} = \mathbf{6.0000\ \Omega}
  2. 2Power: P=V×I=12 V×2 A=24.0000 WP = V \times I = 12\text{ V} \times 2\text{ A} = \mathbf{24.0000\text{ W}}

Formula & Theory

V = I × R | P = V × I = I²R = V²/R

Ohm's Law defines the direct relationship between potential difference (voltage), electric current, and resistance in a DC circuit or purely resistive AC circuit.

Variable Definitions
V:
Voltage (Volts (V)) – Electrical potential difference across the circuit
I:
Current (Amperes (A)) – Flow rate of electric charge
R:
Resistance (Ohms (Ω)) – Opposition to electric current flow
P:
Power (Watts (W)) – Rate of electrical energy conversion

Worked Engineering Example

12V Automotive Circuit

A 12V automotive circuit powers a 4Ω resistive headlight bulb.

Inputs:
  • Voltage: 12 V
  • Resistance: 4 Ω
Result: Current = 3.00 A, Power = 36.00 W

Key Assumptions

  • •Conductor temperature remains constant during measurement.
  • •Circuit is purely resistive (zero reactive inductance or capacitance).
  • •Linear ohmic behavior is assumed across the operating range.

Limitations & Safety Scope

  • •Does not account for reactive AC impedance (Z) with phase angle shifts.
  • •Non-linear semiconductor devices (diodes, transistors, thermistors) do not follow fixed Ohm's Law resistance.

Frequently Asked Questions

What is Ohm's Law?

Ohm's Law states that the current passing through a conductor between two points is directly proportional to the voltage across the two points and inversely proportional to the resistance.

Can Ohm's Law be used for AC circuits?

Yes, for purely resistive AC loads. For circuits with inductors or capacitors, impedance (Z) and phase angle (cos θ) must replace simple DC resistance.

Related Calculators & Engineering Tools

Power Calculator
Current Calculator
Resistance Calculator
Voltage Drop Calculator
Ohm's Law Reference Guide
Electrical Formulas Sheet
How to Calculate Power

Educational & Reference Notice: This calculator provides technical estimates based on standard physical formulas. Actual electrical installation, protective device sizing, and conductor selection must be verified against the applicable electrical code (NEC, IEC, CEC) by a licensed electrician or qualified professional engineer.