Ohm's Law Calculator
Calculate voltage, current, resistance, or power using Ohm's law: V = I × R and P = V × I.
What is Ohm's Law Calculator?
The Ohm's law calculator handles the fundamental electrical relationship V = IR, plus power P = VI.
Formula
V = I × R. P = V × I. Solve for any one if you know any two.
Worked example
A 12 V battery driving 2 A draws 24 W and sees a 6 Ω resistance.
How to use this calculator
- Enter any two of voltage, current, resistance.
- Leave the third blank.
- All four values appear (including power).
Frequently asked questions
What's the difference between voltage and current?
Voltage (V) is electrical "pressure" — the force pushing electrons. Current (A) is the flow rate of electrons. Resistance (Ω) is what opposes the flow. Voltage is potential difference; current is the resulting motion.
How dangerous is it?
Current kills, not voltage per se. 0.05 A through the heart can be fatal. A 9V battery has plenty of voltage but draws too little current to be dangerous through skin. House mains (120-240 V) is dangerous because of the available current.
What's a typical household resistance?
A 60 W bulb on 120 V: I = P/V = 0.5 A. R = V/I = 240 Ω. A laptop charger drawing 65 W on 120 V: ~220 Ω.
How does this apply to circuits?
For series circuits, resistance adds. For parallel, the reciprocals add. This calculator is for single-resistance circuits.