Categories⚡ Engineering & EnergyOhm’s Law Calculator

Ohm’s Law Calculator

Calculate Voltage (V), Current (I), Resistance (R), and Power (W).

Fill in any two values to solve for the third:
Voltage
12 V
Current
2 A
Resistance
6 Ω
Power
24 W
Guide & Educational Reference
How to Use the Ohm's Law Calculator
  1. 1Enter any two values among Voltage (V), Current (A), and Resistance (Ω).
  2. 2Leave the parameter you want to solve for blank.
  3. 3View the computed unknown value and the calculated DC power output in Watts (W) instantly below.
What Is Ohm's Law?

Ohm's Law defines the fundamental electrical relationship between electric potential (Voltage, V), electric current (Current, I), and opposition to current flow (Resistance, R) in a DC linear circuit. Named after German physicist Georg Ohm, it states that current through a conductor is directly proportional to voltage and inversely proportional to resistance.

Formulas Implemented by THE CALC
Voltage (V)

Calculated when Current (I) and Resistance (R) are provided.

V = I × R
Current (I)

Calculated when Voltage (V) and Resistance (R) are provided.

I = V / R
Resistance (R)

Calculated when Voltage (V) and Current (I) are provided.

R = V / I
DC Power Output (P)

Automatically calculated for all valid pairs.

P = V × I
Practical Real-World Example
12V Automotive Circuit
Input: Voltage = 12 V, Resistance = 6 Ω → Current I = 12 / 6 = 2 A. Power P = 12 × 2 = 24 W.
→ Current = 2.00 A | Power = 24.00 W
Find current: 9 V across 3 Ω (leave current blank)
I = V / R = 9 / 3 = 3 A; Power P = V × I = 9 × 3
→ 3 A; 27 W
Find voltage: 0.5 A through 100 Ω (leave voltage blank)
V = I × R = 0.5 × 100 = 50 V; Power P = V × I = 50 × 0.5
→ 50 V; 25 W
Important Assumptions & Considerations
  • Linear DC model: Assumes ideal linear ohmic resistance without temperature-dependent resistance shifts or AC reactance.
  • Division by zero: If Current (I) or Resistance (R) is set to 0 when solving for the other, the calculation is undefined (returns no result).
  • Power context: The power result P = V × I represents ideal DC power. For AC circuits with reactance and power factor, use the Electrical Power Calculator.
Frequently Asked Questions

What units does this calculator use?

Voltage is in Volts (V), Current is in Amperes (A), Resistance is in Ohms (Ω), and Power is in Watts (W).

Why does the calculator return no result when entering 0 for resistance?

Solving for Current when Resistance is 0 requires dividing Voltage by 0 (I = V / 0), which is mathematically undefined.

How many values do I need to enter?

Exactly two of Voltage, Current, and Resistance. Leave the third field blank and the calculator solves for it, then also reports DC power (P = V × I).

Why do I sometimes get no result?

Solving for current or resistance divides by the other, so a zero in that field makes the result undefined and the calculator returns nothing.

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