Ohm's Law states V = I × R. The current through a conductor is proportional to the voltage and inversely proportional to the resistance.

How many values do I need to enter?

You need exactly 2 known values. The calculator will solve for the other 2 unknowns.

WHOLE

CALCULATOR

Ohm's Law Calculator

Enter Any 2 Values

Leave unknowns blank — they will be calculated automatically.

Voltage (V)

Current (I)

Resistance (R)

Power (P)

Ohm's Law Formula Wheel

I × R

P / I

√(P × R)

V / R

P / V

√(P / R)

V / I

V² / P

P / I²

V × I

V² / R

I² × R

Ohm's Law Calculator: Compute Voltage, Current, Resistance & Power

Our Ohm's Law Calculator lets you find any two unknown electrical quantities when you provide the other two. Enter any combination of Voltage (V), Current (I), Resistance (R), or Power (P), and the calculator instantly solves for the remaining values using Ohm's Law and the power equation.

Ohm's Law is the foundation of electrical engineering. It states that the current through a conductor is directly proportional to the voltage across it and inversely proportional to its resistance: V = I × R. Combined with the power formula P = V × I, these two equations can solve virtually any basic DC circuit problem.

This tool is essential for electricians, electronics hobbyists, students, and engineers who need quick calculations for circuit design, troubleshooting, and component selection.

Understanding Ohm's Law

Ohm's Law was formulated by German physicist Georg Simon Ohm in 1827. It describes the relationship between voltage, current, and resistance in a linear, resistive circuit. The law holds true for circuits containing only resistive elements, whether the voltage is DC or AC.

The three primary forms are: V = I × R (voltage equals current times resistance), R = V / I (resistance equals voltage divided by current), and I = V / R (current equals voltage divided by resistance).

Electrical power (P) is the rate of energy transfer, measured in watts. Joule's Law combined with Ohm's Law gives us: P = V × I, P = I²R, and P = V²/R. Our calculator uses all of these relationships to solve for any unknown.

How to Use the Ohm's Law Calculator

Step 1: Enter any two values: Provide Voltage (V), Current (A), Resistance (Ω), or Power (W) — any two of the four.
Step 2: Leave unknowns blank: The fields you want to calculate should be left empty.
Step 3: Calculate: Click the Calculate button to instantly see all four values.
Step 4: Review formulas used: The calculator shows which equations were applied.

Ohm's Law & Power Formulas

Ohm's Law

V = I × R | I = V / R | R = V / I

The fundamental relationship between voltage (V), current (I), and resistance (R).

Power Equations

P = V × I | P = I² × R | P = V² / R

Power (P) in watts can be derived from any two of V, I, and R.

Derived Relationships

V = √(P × R) | I = √(P / R) | R = P / I² | V = P / I

All 12 possible combinations from the Ohm's Law formula wheel.

Example Calculations

Known	Values	Calculated	Results
V & I	V=120V, I=2A	R & P	R=60Ω, P=240W
V & R	V=9V, R=100Ω	I & P	I=0.09A, P=0.81W
I & R	I=0.5A, R=220Ω	V & P	V=110V, P=55W
V & P	V=240V, P=1000W	I & R	I=4.17A, R=57.6Ω

Benefits of Our Ohm's Law Calculator

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Any-Two Solver
Calculate any two unknowns from the other two — all 6 input combinations supported.
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Formula Wheel
Built-in visual formula wheel showing all 12 relationships between V, I, R, and P.
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Instant Results
Real-time calculation as you type — no need to press a button.
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Educational
Shows the formulas used for each calculation, perfect for learning.