Ohm's Law Calculator

V = I × R, P = V × I - Calculate any value

Formula

V = I × R. P = V × I = I² × R = V² / R. R = V / I. I = V / R = P / V. V = P / I.

Ohm's Law defines the relationship between voltage, current, and resistance in a conductor. Power formulas derive from P = VI. All calculations assume DC or purely resistive AC.

How to Calculate Manually

1
Select which two values you know
2
Enter the values with units
3
Calculator computes the other two
4
Shows all four: V, I, R, P

Reference Table

Scenario	Formula	Example
Find Current	I = V / R	120V / 12Ω = 10A
Find Resistance	R = V / I	120V / 10A = 12Ω
Find Voltage	V = I × R	10A × 12Ω = 120V
Find Power (VI)	P = V × I	120V × 10A = 1200W
Find Power (I²R)	P = I² × R	10² × 12 = 1200W
Find Power (V²/R)	P = V² / R	120² / 12 = 1200W

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

Ohm's Law is the fundamental principle governing electrical circuits. Discovered by Georg Ohm in 1827, it states that the current through a conductor is directly proportional to the voltage across it and inversely proportional to its resistance: V = IR. This simple equation, combined with the power formula P = VI, allows you to solve for any electrical quantity when you know any two...

Frequently Asked Questions

What is Ohm's Law? V = I × R. Voltage = Current × Resistance. P = V × I = I² × R = V² / R. The foundation of electrical circuit analysis.: V = I × R. Voltage = Current × Resistance. P = V × I = I² × R = V² / R. The foundation of electrical circuit analysis.
What are the units? V = volts, I = amperes (amps), R = ohms (Ω), P = watts (W). 1 A = 1000 mA. 1 kΩ = 1000 Ω. 1 kW = 1000 W.: V = volts, I = amperes (amps), R = ohms (Ω), P = watts (W). 1 A = 1000 mA. 1 kΩ = 1000 Ω. 1 kW = 1000 W.
Does this work for AC circuits? For resistive loads, yes. For inductive/capacitive loads, use impedance Z instead of R, and consider power factor. V = I × Z.: For resistive loads, yes. For inductive/capacitive loads, use impedance Z instead of R, and consider power factor. V = I × Z.

Calculator

Formula

Formula

How to Calculate Manually

Reference Table

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

Frequently Asked Questions

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