Ohm's Law Calculator
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Ohm's Law & Power Formula Reference
Voltage (V)
The electrical pressure that drives current through a circuit. Measured in volts (V).
- V = I × R
- V = P ÷ I
- V = √(P × R)
Current (I)
The flow of electric charge through a conductor. Measured in amperes (A).
- I = V ÷ R
- I = P ÷ V
- I = √(P ÷ R)
Resistance (R)
How much a material opposes the flow of current. Measured in ohms (Ω).
- R = V ÷ I
- R = V² ÷ P
- R = P ÷ I²
Power (P)
The rate at which electrical energy is used or produced. Measured in watts (W).
- P = V × I
- P = V² ÷ R
- P = I² × R
About This Tool
Ohm's Law is one of the most fundamental principles in electrical engineering and physics. It describes the relationship between voltage, current, and resistance in a circuit: V = I × R. This tool extends that relationship to include power, giving you 12 formulas across all four variables — voltage (V), current (I), resistance (R), and power (P).
How to use it:
- Pick what you want to solve for
- Choose which formula to apply
- Enter two known values and hit "Calculate"
Along with the answer, you'll see the full formula with your numbers plugged in, plus the remaining values computed automatically. Whether you're a student working through a physics problem or an engineer double-checking a circuit, this tool gets you there in seconds.
Ohm's Law and Power
Ohm's Law — V = I × R — tells you that voltage equals current times resistance. Rearrange it and you can solve for any of the three. Bring power into the picture with P = V × I, and a whole set of derived formulas opens up, letting you find any value from any two others.
A quick note on symbols: in formulas, power is represented by P, while its unit is the watt (W). Voltage uses V for both the symbol and the unit, and current is I (from the French "intensité"), measured in amperes (A). Resistance is R, measured in ohms (Ω). You may occasionally see E used for voltage in older American textbooks — it stands for electromotive force — but V is the modern standard.
Quick Example
A 120V outlet powering a 60W light bulb: the current drawn is I = P ÷ V = 60 ÷ 120 = 0.5 A, and the bulb's resistance is R = V ÷ I = 120 ÷ 0.5 = 240 Ω.